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1927 Map of the Arboretum

Past Tree Mobs™

2020 | 2019 | 2018 | 2017 | 2016

2015 | 2014 | 2013 | 2012


TreeMob™! Behold the Beautybush

May 2020

Join Michael Dosmann, Keeper of the Living Collections, for a presentation about one of explorer E.H. Wilson’s favorite horticultural introductions from China. Michael will speak from the Arnold landscape about the story of the arrival of Kolkwitzia amabilis in North America, how it grew in popularity, and its current status in its native habitat. View this Tree Mob on our YouTube channel.

TreeMob™! Zooming in on Tree Swallows

May 2020

Though circumstances are currently strange for humans, birds are carrying on as usual. This means that the Arnold Arboretum’s NestWatch volunteers have been making the rounds of various nesting boxes, installed in the Arnold Arboretum’s landscape. They are recording observations of “house-shopping,” territorial battles, nest-building, and egg-laying. Karla Noboa, a second-season NestWatch monitor and avid birder, will speak about this program and what she has recorded at one of the tree swallows’ abodes. View this Tree Mob on our YouTube channel.

When not monitoring nests, Karla Noboa is Community Engagement Manager with River Network. She started the Feminist Bird Club Boston Chapter and serves as chapter network chair on the Feminist Bird Club board of directors.

TreeMob™! Zooming in on Spruce Cones

May 2020

Join Arnold Arboretum Director William (Ned) Friedman for a long-distance Tree Mob. Ned will speak from the Arnold landscape about the beautiful color, morphology, and reproductive biology of spruce (Picea sp.) cones. We invite you to join us on screen via Zoom for this remote tree mob. View this Tree Mob on our YouTube channel.

TreeMob™! Hamamelis Happens

March 2020

We’ve been enjoying witch hazel blooms since January however March is when our Hamamelis sp. collection truly makes its presence known. A concentration of wavy and curling petals in shades of red, orange, yellow, and maroon induces us to admire. When we inevitably bring our noses close, we experience a variety of delicious scents. Gather on Meadow Road at Acc. # 50-2019*A Hamamelis mollis ‘Iwado’ at 3:00pm on Thursday, March 5. Head of Horticulture Andrew Gapinski will showcase one of his favorite Arboretum collections.

TreeMob™! Whoooo’s In the Arboretum?

January 2020

January afternoons and evenings are a perfect time to listen and look for Great Horned Owls. In the lead up to their nesting season, this charismatic and formidable species is often heard calling throughout the Arboretum’s collections. Join Brendan Keegan, Arboretum Gardener, to learn about Great Horned Owls, how to go owling ethically, and possibly hear and see a few owls as well. Please dress warmly and bring a flashlight..


TreeMob™! Diversity and Dispersal Among Viburnums

November 2019

Autumn is a great time to appreciate the beauty of viburnums, with their vibrantly colored fruits and leaves. Join Wendy Clement to explore the diversity of viburnums and the hidden features of their leaves and fruits that facilitate interactions with other organisms in their communities. Hear about the important role the living viburnum collections at Arnold Arboretum have played in notable studies on the diversity, classification, ecology, and evolutionary history of this group. See for yourself why horticulturalist Michael Dirr wrote: “A garden without Viburnum is akin to life without music or art”!

TreeMob™! Respecting Your (Box) Elders

October 2019

Small in stature and without showy foliage, the Arnold’s seven box elder (Acer negundo) trees are rarely even recognized as members of the maple genus! But these “ash-leaved maples” are more than just weedy street trees. In fact, these jewels among the Arboretum’s internationally recognized maple collection constitute perhaps the most unusual and evolutionarily distinct species in the genus. Join us at tree Acc. # 253-2013*A (about 10 minutes from the Hunnewell Building) for a whole new perspective on the ecology and evolution of the humble box elder and its place among the Arnold’s marvelous maples.

TreeMob™! From Solar Power to Flower Power

September 2019

With a projected completion date in fall 2019, the Weld Hill Solar Project represents the Arnold Arboretum’s most ambitious sustainability initiative to date. Comprising nearly 1300 solar panels, the system is capable of producing an estimated 566,409 kWh annually (approximately 30% of the Weld Hill Research Building’s total energy load). Working in tandem with the panels, a unique battery storage array reduces peak demand charges, adding additional energy savings. Join Danny Schissler to learn about the photovoltaic system and Brendan Keegan to hear about the initial stages of development of a native plant pollinator meadow within the area of the solar panels. Meet at the solar array behind the Weld Hill Building at 1300 Centre Street, Roslindale. Off-street parking is available. Find directions on our website under “Visit.”

TreeMob™! Of Worms and Forests

September 2019

Do you know that New England has no native earthworm species? Or that these amazing organisms, much loved by farmers and gardeners, threaten northern forest ecosystems? Or climate change models are being revised upward to account for their unseen, but industrious, productivity? If not, join us to consider the mighty earthworms with Arnold Arboretum gardener Brendan Keegan. You’ll learn some simple tricks for finding and identifying earthworms, examine a few truly invasive species, and discuss the role these incredible creatures play in our yards, gardens, and forests. Meet at Acc. # 365-2014*E, Aesculus pavia, on September 18, at 4:00 p.m. We’ll mover from there into the nearby North Woods in search of worms and evidence of their efforts.

TreeMob™! Hemlock Hill–Enhancing Access

August 2019

The Arboretum’s 2019 Isabella Welles Hunnewell Interns just completed their group project, an annual requirement for the internship in public garden horticulture, arboriculture, plant production, and curation. This year’s project focused on visitor and educator access to Hemlock Hill, one of four natural woodlands in the Arboretum landscape. Their research included questions such as: what is a native hemlock forest? How do visitors use this hill? How and why is the area used in the Arboretum’s school programs? And how should the site be improved? The resulting proposal serves a plethora of demands while maintaining and improving the biodiversity of life on the hill. Meet on Hemlock Hill Road at Taxus cuspidata (Japanese yew), Acc. # 1704*C , Wednesday, August 14 at 2:00pm.

TreeMob™! Following the Swallows

August 2019

This spring, the Arboretum launched NestWatch, a new citizen science initiative to collect data on birds that breed in the Arboretum. Program volunteers monitored black-capped chickadee, tree swallow, eastern bluebird, and house wren nests across 30 nesting boxes. Breeding birds face myriad obstacles and challenges in raising a successful brood of young, and this year’s cool and rainy spring was no exception. NestWatch volunteer Justine Hanson will share her experiences observing a tree swallow (Tachycineta bicolor) family throughout the breeding season, from courtship and nest-building to young fledglings taking their first flight. Meet at 6:00pm on Thursday, August 8, on Meadow Road at Acc. # 13232*B Phellodendron amurense var. amurense.

TreeMob™! ¡Pon un insecto en tu vida! Put a bug in your life!

July 2019

Los insectos causan sentimientos enfrontados, desde horror y fobia hasta la más absoluta fascinación. Pero independientemente del sentimiento que despierten, están muy presentes en nuestra vida diaria. Y sin embargo, podrían desaparecer en apenas un siglo si no se toman medidas para protegerlos y conservarlos. Pero ¿qué importancia tiene la desaparición de “esos pequeños seres”? ¿Podemos vivir sin ellos? De todo esto y mucho más se tratará en este móvil Tree Mob en el que, armados de cazamariposas y tras un breve entrenamiento con la entomóloga Tatiana Pina, los asistentes podrán sentirse entomólogos por un día, acercarse a la inagotable diversidad de los insectos y conocer los principales grupos de nuestro entorno, así como descubrir qué papel juegan.

TreeMob™! Black Swallow-wort Biocontrol

July 2019

Black swallow-wort (Vincetoxicum nigrum) is a hardy European vine which sits high on the list of Massachusetts’ most disliked exotic invasive plant species. Growing in full sun to partial shade and found in all regions of the state, black swallow-wort can easily overwhelm a community of plants. The University of Rhode Island (URI) is conducting research using an insect, Hypena opulenta, to control the spread of swallow-worts and the Arnold Arboretum is participating as one of the release sites. Come hear entomologist Lisa Tewksbury and coastal fellow intern Lexi Johnson, both with URI, speak about the plant, the insect, and the use of a biological control for invasive weed management. Meet near the Mendum Street Gate on Peters Hill at Acc. # 601-2017*A (Quercus sp.) on Monday, July 15, at 6:00 p.m.

Note: Wear non-sandal, closed-toe shoes. The area includes poison ivy which has been mowed, but we still recommend that you wear enclosing footwear.

TreeMob™!ree Mob™! Why Trees?

July 2019

With decades of study in tropical biology, ethnobotany, evolution, ecology, and conservation, Dr. W. John Kress insists that we learn about the common trees around us. But he’d like us to delve deeper than just tree names. “Knowing the name of a tree is one of the most important things that helps us understand how trees grow, how they evolved, how they fit into the communities of nature where they grow, and the value that they provide to us.” Join us at Acc. # 22882*B Liriodendron tulipifera (tulip tree or yellow poplar) at 6:00pm on Thursday, July 11 as John explains the importance of trees to our lives and the planet and how our efforts to protect them become more critical each day. You may already support conservation, but John will inspire you towards greater commitment and necessary action.

TreeMob™! What Tilia Can Tell Us

June 2019

Dr. Elizabeth (Lizzie) M. Wolkovich, Associate Professor of Forest & Conservation Sciences at University of British Columbia, returns to the Arnold Arboretum for a phenology update. She will discuss how leafing times, flowering times, and fruiting times are related — or if there isn’t really much of a relationship for some trees — and why it matters. Meet on Peters Hill at Acc. #1323-82*A Tilia americana (American basswood), a species on the Peters Hill Tree Spotters route, on Wednesday, June 5th at 4:30pm. Park along Bussey Street, keeping your tires off the sidewalk, and follow signs to the mob.


TreeMob™! ‘Tis the Season…to admire a tree

December 2018

Elizabeth (Lizzie) Wolkovich has traveled eastward from British Columbia to speak again about citizen science that tracks tree phenology at the Arnold Arboretum. She’ll share data that indicate that changing climates are affecting phenophases such as budburst and leafout in trees, and seed-sprouting and dormancy in woody plant seeds. Using several years of results from the Arboretum’s Tree Spotters program, Lizzie will explain how and why arboreta are such valuable resources for researchers. We will meet with her at Acc. 358-82*A, Quercus alba, a white oak originally from Georgia, and compare it to a neighboring oak, native to the Arnold Arboretum, to consider the role of genes and environment in the lives of these two specimens. Gather on Thursday, December 20 at 3:00pm on Valley Road at Acc. # 358-82*A to admire and compare these trees.

TreeMob™! Migration Magic

November 2018

Visit Albizia julibrissin (silk tree or mimosa) with the Arnold Arboretum’s resident birder Bob Mayer to learn about some of the avian migrants who feed in this arboreal oasis on their travels, either north or south. You will likely see blackpoll warblers, yellow-rumped warblers, ruby-crowned kinglets, and more. Even a Cape May warbler is a slight possibility, as one was sighted recently in this tree. Join us to learn why these birds have chosen this particular tree. Meet at Accession 125-35*A on Bussey Hill Road, opposite the entrance to the Explorers Garden at 12:15pm on Thusday, November 1. Bring binoculars if you have a pair.

TreeMob™! What’s Up with Chestnuts

September 2018

Putnam Fellow Elizabeth (Beth) Spriggs, PhD, will speak about the phylogeny and biogeography of chestnuts. Meet on Valley Road to look at several species, learn where they are from, and how the chestnuts are related. She will explain the co-evolution of the chestnut blight (Cryphonectria parasitica) with the Asian species, its introduction to North America in the early 20th century, and the continuing effect of the blight today. At the Arnold Arboretum, Beth is conducting genomic research on the chestnuts and ashes (Castanea and Fraxinus) – iconic, but severely threatened North American trees—to inform future conservation strategies. Meet near the rockery on Valley Road at Accession 24-80*A, Castanea dentata, at 5:45 on September 27.

TreeMob™! 2018 Intern Project Presentation

August 2018

Just finishing their summer at the Arboretum this month, the Isabella Welles Hunnewell Interns will share the results of their group project via a Tree Mob. Join us at the Walter Street Gate to learn about its history and plantings, and hear the interns’ suggestions for improving this vital portal to the Arboretum. Meet at the Walter Street Gate at 2:30pm, on Tuesday, August 14.

TreeMob™! Make More Plants

July 2018

For some of us, there is nothing more satisfying than generating more plants. If you identify with this pleasure, then join this tree mob with Arnold Arboretum Plant Propagator Sean Halloran. Sean will discuss several methods of tapping into a plant’s reproductive attributes to duplicate what’s growing in your yard or what you covet from your neighbor’s garden. Meet at the Dana Greenhouse and Nursery Facility on Wednesday, July 18 at 6:00pm to get a quick overview of air layering, softwood and greenwood cuttings, and ways to do all of this without a greenhouse!

TreeMob™! Sunshine on a Solar Array

June 2018

The Arnold Arboretum is the home of a living collection of over 15,000 individual plants, but there are other – also very interesting – living organisms that inhabit this space. One such organism makes its home on solar panels recently installed on the roof of the Arboretum’s equipment garage. Over the last few months Kristie Sylvia Araceli Tanner has been studying these micro-organisms. Despite the harsh environmental conditions that these surfaces are exposed to (temperature fluctuations, irradiation, and desiccation), solar panels harbor a high amount of pigmented bacteria. Join us at this Tree Mob to learn about the range of applications for these unseen organisms…and how they may color your future. Meet at the staff patio behind the Hunnewell Building on Thursday, June 21 at 6:30pm. Follow signs from the Hunnewell Building to the location.

TreeMob™! Bird Housing Market Analysis

May 2018

Cities can be hard places for cavity dwelling birds to find a home. Arboretum landscape crew members Jed Romanowiz, Nima Samimi, and Brendan Keegan constructed a variety of new bird houses over the winter to provide more nesting sites for these species in the Arboretum. Since then, Brendan has been monitoring home sales, move-in dates, and occupancy permits. At this Tree Mob, he will share what he has observed about nest-building, egg-laying, incubation, and neighborhood dynamics. Meet at the edge of Kent Field, the meadow below the Conifer Collection, near Acc. # 1476*B Picea pungens (Colorado spruce) on Thursday, May 31 at 6:00pm to get a birds-eye view of urban housing.

TreeMob™! Lizzie’s Back: An Update on Phenological Data

May 2018

Elizabeth Wolkovich, PhD, recently an Arnold Arboretum researcher, and now heading up the Wolkovich Group of the Temporal Ecology Lab at the University of British Columbia, is back in town for a visit. She wants to reunite with the Arboretum’s volunteer Tree Spotters (a program which she initiated) to provide insight on how researchers use data collected by Tree Spotters and discuss her work in temporal ecology. Join Lizzie for a Tree Mob/Botany Blast on Peters Hill on Monday, May 14 at 4:30pm, at Acc. #16611*F Populus deltoides ssp. deltoides (Eastern Cottonwood). If it rains, the event will take place at the Weld Hill Research Building. Plan to arrive early or stay afterwards to admire the crabapples in bloom.

TreeMob™! Beeches–Drastic Measures in Collections Management

April 2018

When managing a living collection of plants, one deals with destructive pests and diseases as well as natural aging and variable weather conditions. This can necessitate tough decisions. In the case of the Arboretum’s Beech Collection, Arnold Arboretum collections stewards have recently taken drastic measures, removing a large number of beech (Fagus spp.) trees. Infected with beech bark disease, some of the oldest beeches in the Arboretum have gone into decline. Caused by an exotic sap-feeding scale insect (Cryptococcus fagisuga) and a secondary infection of two fungi species (Neonectria spp.), beech bark disease poses an ecological threat to forest and cultivated trees throughout the Northeast. In order to combat this destructive disease here at the Arboretum, heavily affected and failing trees–sources of fungal inoculum–are being removed from the collections. Join Andrew Gapinski, Manager of Horticulture, and others on Tuesday, April 24 at 3:00pm to learn about current and future efforts to keep the beeches as healthy as possible. Meet at the intersection of Hemlock Hill Road and Beech Path at Acc. # 290-93*A European beech (Fagus sylvatica).

TreeMob™! The Power of Snowdrops

March 2018

What has milk-white flowers, purportedly protects from witches, and drives some people mad? Snowdrops (Galanthus), of course! Let’s celebrate the passing of winter with the emergence of these harbingers of spring. Drop on by to learn how an ancient, floral folklore informed science and how to grow these little jewels for yourself. Gather with Terry Huang, Living Collections Fellow of the Arnold Arboretum, on Thursday, March 29 at 3:30pm on Beech Path at Acc. # 22885*A.


TreeMob™! Medlars Maligned

December 2017

In this image of a medlar (browned out blob of a shrub on the right), there is nothing redeeming except for the three contrails that were converging at the time that I took the photo. And in literature too, there is little to be found that describes the fruit of the medlar in words that I wish to use here (see Shakespeare’s Romeo and Juliet, Act 2, Scene 1, page 2). Medlar (Mespilus germanica) is a rosaceous shrub of southwest Asia and southeastern Europe, historically common in European gardens, but rarely cultivated in the United States. To be edible, the fruit must blet, or decay, to the stage at which it looks like a mealy, brown, rotten apple. Not until then does it become an applesauce-like, sweetish “delight.” Join us for a Tree Mob in the Bradley Rosaceous Collection at Acc. # 727-89*C on Thursday, December 7 at 2:00pm, to hear Living Collections Fellow Robert Dowell’s take on this oddity of antiquity and, perhaps, some of its uncouth nicknames.

TreeMob™! A Halloween Horror

October 2017

Come if you dare, wearing costumes with flare,
To the lilacs that live at the Arnold.
At a quarter past noon, you’ll see lilacs in bloom
alongside ghoulish, biological horrors.
Of phytoplasmas we’ll speak, those bacteria gone freak,
causing branches to form witches’ brooms.

TreeMob™! Walking Wilson’s Legacy

October 2017

Self-proclaimed itinerant photographer Scott Dietrich will lead this traveling Tree Mob through the Arnold Arboretum landscape, comparing trees in the Arboretum’s Living Collections with photographs of those species taken by explorer E.H. Wilson. In the first decade of the 20th century, Wilson was hired by the Arnold Arboretum to collect plants from China, Japan, and Southeast Asia and was sent there with a camera to document his journey. The Arnold Arboretum holds an archive of over 7,000 of Wilson’s photographs. Scott, who is working on a book of Wilson’s legacy, will begin this tour at the Hunnewell Building and finish on Bussey Hill in the Explorers Garden, connecting some of Wilson’s photographs with stories of discovery and the trees he collected. This traveling Tree Mob will last approximately 1 hour. Meet at the Hunnewell Building at 1:00pm on Saturday, October 28.

TreeMob™! 3-D Printing of Bamboo

October 2017

Massachusetts Institute of Technology Professor Lorna Gibson studies the mechanical behavior of materials, specializing in materials with a cellular structure, such as engineering honeycombs and foams, scaffolds for regenerative engineering, and natural materials such as wood, bamboo and plant leaves and stems. Lorna will speak about a project in which plant structures are used as models to improve the strength of structural construction products. In this case, she used computed tomography and 3-D printing to make models of parenchyma tissues in bamboo, tinkering with cellular wall thicknesses to determine optimum performance. Join this Tree Mob on Thursday, October 12 at 3:00pm at Acc. # 2267*A, Carya cordiformis (bitternut hickory), to view two types of bamboo and learn about ways that plants are used in structural engineering.

TreeMob™! Soil Analysis Across Acres

September 2017

Living Collections Fellow Jenna Zukswert is in the midst of a multi-year project to assess the soils of the Arnold Arboretum. What began with a general survey by our 2015 Hunnewell Interns has evolved into an all-consuming effort to understand the A and B soil horizons across the entire Arboretum. She and her colleagues have consulted with a committee of experts from the USDA, academia, and the USFS, and have strategically collect soil samples for analysis from 120 different zones in the landscape. In conjunction with soils, Jenna is measuring nutrients in foliage from three tree species to better understand foliage-soil relationships and the uptake of nutrients. Attend a tree mob to learn about this project with its ultimate goal of ensuring the health of the Arboretum’s 15,000-plus plants. Gather on Wednesday, September 27, at 2:30pm to learn about this project with its ultimate goal of ensuring the health of the Arboretum’s 15,0000-plus plants. Meet at Acc. # 18054*E, Quercus alba, on Oak Path.

TreeMob™! Air-layering

August 2017

On the edge of our maple collection stands a specimen of Acer diabolicum, collected by the Arboretum’s first director, Charles Sprague Sargent, and accessioned into the living collections in 1892. Hailing from a mountain forest in Hakone, Japan, the tree has proved difficult to propagate by stem cuttings. To ensure the genetic heritage of this particular plant, our staff is testing a propagation method called air-layering. Come learn about this age-old process, in which roots are generated on a living branch, and the next steps in cultivating air-layered stems. Meet with Living Collections Fellow Robert Dowell at our younger test subject, Acer diabolicum Acc. # 630-77*A, on Tuesday, August 22 at 4:15pm.

TreeMob™! Mallow Out

August 2017

Hibiscus moscheutos ssp. palustris (marsh mallow or sea hollyhock) stands tall with large-petalled pink flowers along the banks of Dawson pond in August. Nancy Rose, horticulturist and editor of Arnoldia, will speak about this herbaceous perennial and another Hibiscus species found at the Arboretum, the woody shrub Hibiscus syriacus (Rose of Sharon). Both are in the Malvaceae as is Althaea officinalis, the root of which was originally used to make the confection known as marshmallow. Always eager to acknowledge a plant’s contributions to our dietary pleasures, we will celebrate the Malvaceae and the 100th anniversary of locally-made Marshmallow Fluff. Join Nancy Rose and Pam Thompson, Manager of Adult Education, on the shore of Dawson Pond (at Acc. # 1724-81*MASS, H. moscheutos ssp. palustris), on Monday, August 14 at 5:30pm.

TreeMob™! Managing the Herbaceous Layer

August 2017

The Arboretum’s 2018 Isabella Welles Hunnewell Interns just completed their group project, an annual requirement for the internship. This year’s interns assessed the herbaceous layer in the Linden and Beech Collections. Their assessments will inform management strategies to improve soil health and specimen vitality in both areas. Join the interns in the Lindens to hear about their research, discoveries, and recommendations. Meet at Acc. # 722-53-A, Tilia japonica, on Wednesday, August 9 at 2:30pm.

TreeMob™! Flowers–Lavish or Minimalist?

July 2017

Flowering requires water to support floral tissue expansion and physiology. However, several temperate tree species flower as they come out of dormancy when they have a decreased capacity for water transport. Natalie McMann, a Masters student at the University of Minnesota Duluth, accompanied by Arnold Arboretum Sinnott Award researcher Jessica Savage, will explain how size affects flower water use and discuss how trees may be able to flower when water is a limiting resource. Meet near the Arborway Gate at Acc. # 779-87*B, Magnolia virginiana x virginiana ‘Milton’, at 12:15pm on Thursday, July 27.

TreeMob™! Hosting the Pipevine Swallowtail

July 2017

We often see butterflies sipping nectar from flowering plants, but many species lay their eggs on very specific host plants. Learn about the special relationship between the Dutchman’s pipevine (Aristolochia macrophylla), growing near the Hunnewell Building, and a swallowtail butterfly (Battus philenor), recently discovered in the Arnold Arboretum. Meet with Arboretum Docent Bob Mayer at the Hunnewell Building on Tuesday, July 18 at 5:00PM. The mob will take place at the rear of the building on the Staff Patio.

TreeMob™! Bee Hospitable

June 2017

The industrious honeybee, supporting its busy hive, is a classic example of a hardworking summer pollinator and of bees in general. However over 85% of bee species do not live in hives at all. For example, solitary bees make or inhabit burrows in wood, rock walls, or soil. There, they lay eggs and store food, creating a safe home for their offspring until they emerge the following year. Attend this Tree Mob with Arboretum Gardener Brendan Keegan on Tuesday, June 20 at 4:00pm to learn more about solitary bees and how you can create habitat for them in your backyard or on your balcony. We’ll meet at the Hunnewell Building, either in the lecture hall or on the staff patio, depending on weather. Signs will indicate meeting location.

TreeMob™! Oh My Gracious! It’s Herbaceous!

June 2017At the Arnold Arboretum, we focus our collections on woody plants, but once in a while, we allow something herbaceous into this exclusive club. This has happened since the Arboretum’s early years…as some plants’ charms just can’t be resisted…even by the staunchest of gatekeepers. In this mob, Michael Dosmann, the newly named Keeper of the Living Collections, will show off some of the Arboretum’s hidden herbaceous gems and speak about their provenance and why they are grown and curated here. Meet at the entrance to the Explorers Garden at Bussey Hill Road at 5:30pm on Thursday, June 8, near Rhododendron fortunei, Acc. #1075-89*B. Follow signs from the Arborway Gate or Bussey Street Gate.

TreeMob™! Sargent’s Weeping Hemlock

May 2017

Contradictions, lost or unrecorded facts, and misstatements attributed to Sargent’s Weeping Hemlock (Tsuga canadensis f. pendula) shroud the plant’s origins in mystery. Senior Research Scientist Peter Del Tredici illuminated what has been discovered about this plant by digging into historical records, speculating about locations, and in some cases, taking core samples to count rings. The group met at Acc. # 1514-2*A, a sculptural beauty, on Hemlock Hill Road.

TreeMob™! Syrup from Birches and Other Non-Maples

May 2017

David Moore ran The Crooked Chimney (, a birch syrup production enterprise in Lee, New Hampshire, for several years. He has experience making syrup from maples, birches, walnuts, and sycamores. He will talk about the differences between birch and maple syrup production and also about syruping research he’s been a part of. Meet on the southwest slope of Bussey Hill in the Birch Collection, at Acc. # 12839*A, Betula papyrifera (paper birch), on Tuesday, May 30 at 5:30pm.

TreeMob™! Aronia Hybrids…The Next Novelty Fruit?

May 2017

Interest in Aronia (chokeberry) has increased in recent years because its fruit contains high levels of antioxidants and polyphenols, it is adaptable to various geographic regions, and it has little susceptibility to diseases and pests. It seems like a great match for commercial orchard production, but currently there is little genetic diversity in Aronia grown for fruit production and the fruit has an astringent taste, thus requiring some form of processing before human consumption. Jonathan Mahoney, a PhD student in the Department of Plant Science and Landscape Architecture at the University of Connecticut and and Arnold Arboretum Deland Fellow,  is working on a breeding program to improve Aronia for the commercial fruit industry through intergeneric hybridization. His research group is crossing Aronia with other members of the Pyrinae subtribe within Rosaceae (the rose family) to create novel types of pome fruits for commercial fruit and ornamental crop production. Other important members of the subtribe include Malus (apple), Pyrus (pear), and Cydonia (quince), along with less commonly known fruits including Sorbus (mountain ash), Amelanchier (serviceberry), and Crataegus (hawthorn)—all potential hybridizers with Aronia. Jonathan will demonstrate how he conducts controlled pollinations and discuss some of the reproductive barriers that the breeding program encounters when working with taxa in the Pyrinae subtribe. Gather at Acc. #759-78*C x Sorbaronia dippelii on Willow Path in the Bradley Rosaceous Collection at 4:00pm on Thursday, May 18.

TreeMob™! Arbor Day Planting

April 2017

The Arnold Arboretum’s Campaign for the Living Collections sets forth an ambitious ten-year plan to expand the breadth of plant holdings and increase their scientific and horticultural value. Magnolia acuminata (Acc# 334-2011*A), one of the roughly 400 taxa targeted for addition to the collections in this campaign, is native to eastern North America. Grown in our greenhouse from seed and pampered through various stages of growth, this cucumbertree will now be sited in its permanent home in the Arnold Arboretum’s living collections. Join Horticulturist Greg La Plume and Horticultural Technologist Conor Guidarelli on Arbor Day to celebrate this addition to the Arboretum landscape and learn how to properly plant a tree. Meet in front of the Hunnewell Building at 2:00pm on Friday, April 28.

TreeMob™! To See or Not to See

April 2017

“…the truth of the forest may be more clearly and vividly revealed by the contemplation of a small area than it could by donning ten-league boots, covering a continent but uncovering little.” –David George Haskell, The Forest Unseen

We see a lot in our hectic days, but how much of that do we truly perceive? If we paused for a bit each day in the same spot, what might we learn…about our surroundings, ourselves, other beings? Biologist David George Haskell wondered just that and then followed through on his question. He visited a small plot in a forest, almost daily for a year. What he discovered during an annual cycle of seasons should be incentive for us all to choose to see. Join David in the North Woods to learn about his year of observations and how you too could hone your ecological understanding. Gather at Acc. # 11472*A, Acer truncatum (purpleblow maple), at 5:30pm on Tuesday, April 11. Follow signs from the Arborway gate along Meadow Road to the North Woods dell.

TreeMob™! Worms-the Good, the Bad, and the Ugly

March 2017

What’s good for the garden isn’t necessarily good for the forest. Earthworms, for example, make nutrients accessible to annual and perennial plants in a garden, but disturb nutrient cycling in New England’s forest ecosystems. Most earthworms in New England are exotic, with some considered invasive. Some, like the crazy snake worm (Amynthas agrestis), have the potential to “…change forest structure and the decomposer community in the affected forests,” according to Josef Görres, PhD, at the University of Vermont. At a Tree Mob on Wednesday, March 29 at the Hunnewell Building, Arnold Arboretum Gardener Brendan Keegan spoke about local worms, vermicomposting, and worm management.

TreeMob™! Resin or Not? Plant Exudate

January 2017

Many plants, especially trees, ooze exudates (the gooey stuff, for example, dripping down the trunk of a white pine). Plant exudates include numerous organic products such as resins, gums, and kinos. Smithsonian paleobiologist Jorge Santiago-Blay was collecting samples from the Arnold Arboretum to add to his project to spectrometrically survey the plant exudates of the world. He explained why plants ooze and what that substance can reveal about ancient environments in Earth’s history. The group met in the Hunnewell Building Lecture Hall on Thursday, January 5 at 3:45pm.


TreeMob™! Bark into Golden Hickory Syrup

December 2016

For many from New England, the only syrup approved for pancakes is that which is locally-tapped from a sugar maple (Acer saccharum). However, sap isn’t the only tree source for making syrup. Arboretum horticulturist Sue Pfeiffer took advantage of a downed shagbark hickory (Carya ovata), gathered some bark, and then proceeded to bake and boil. The culinary result was a gorgeous amber-yellow delight. The group met in the Hunnewell Building to learn about turning hickory bark into gold and to taste a sweet sample at 3:45pm on December 14.

TreeMob™! Mechanisms of Mortality: Dwarf Mistletoe along the Maine Coast

November 2016

Eastern dwarf mistletoe (Arceuthobium pusillum), a diminutive plant parasite, can fell a mature white spruce (Picea glauca) in a matter of years. Drawing upon observations at scales from hormone metabolism through whole-tree growth, Barry Logan, a Visiting Scholar from Bowdoin College, proposed a causal chain of events leading to white spruce decline. He related the present-day ecophysiology of coastal Maine spruce stands to patterns of 19th century land use with relevance to the New England region. The group gathered at Accession # 611-93*A, Picea glauca, on Monday, November 7, 2016 at 2:30pm to learn more about this parasitic relationship.

TreeMob™! Radishing, Simply Radishing

November 2016

Vegetables are good for humans, but can trees benefit from them as well? This summer and fall, the Arboretum experimented with growing radishes, a first perhaps, since Benjamin Bussey was farming this land. Living Collections Fellow Jenna Zukswert spoke about the reasons for planting a taproot crop among our trees and whether there will be more vegies in the Arboretum’s future. The group met in the walnut collection at Acc. # 1181*D, Juglans nigra, on Valley Road across from the Centre Street Gate on Tuesday, November 1 at 3:00pm.

TreeMob™! A Unilateral Contract: Epifagus

October 2016

Walking under the beautiful American beech (Fagus grandifolia) on a gorgeous afternoon seems a lovely thing. But do you know that a sinister thief may be present? This freeloader, Epifagus virginiana or commonly beechdrop, is a parasitic plant that forms delicate connections to the roots of American beech trees. The brownish plant has no leaves for photosynthesis and instead depends solely on the tree’s roots for nutrients and water. Zhenzhen Yang, who completed her dissertation at Pennsylvania State University on this monotypic plant, spoke about its life cycle and singular dependence on the American beech. The group met in the beech grove at Acc. # 14585*B on Sunday, October 23 at 2:00pm.

TreeMob™! Meadow Management

September 2016

Kent Field, the grassy meadow that spreads out below the Conifer Collection, provides important habitat for birds, small mammals, and pollinators. Over the past several years, the Arboretum’s horticulture crew (and even staff at an all-staff work day) has been increasing the number and variety of perennial wild flowers that grow in the meadow and along Bussey Brook. Boneset, blue lobelia, asters, and golden rod are currently in bloom and attracting numerous pollinators. Earlier in the season, Joe-Pye weed, sunflowers, milkweed, and cardinal flower added a magnificent display of colors to the area. We heard from Arboretum gardener Brendan Keegan about efforts to broaden the number of meadow species in this area and how the Arboretum manages and expands this landscape as part of an adaptive management approach. The group gathered at Acc. # 351-79*E, Abies sibirica (Siberian fir), on Wednesday, September 28 at 3:45pm.

TreeMob™! Goatscaping

September 2016

In early September, goats became part of the scenery at the Arnold Arboretum, adding a pastoral accent to the already bucolic landscape. But these goats weren’t here, just sitting pretty. They were enlisted to help the Arboretum control invasive plants and overgrown brush…without the use of chemicals. Elaine Philbrick, co-founder of The Goatscaping Company, located at the Colchester Neighborhood Farm in Plympton, MA, spoke about the benefits of using goats to manage landscapes. Pam Thompson, Manager of Adult Education, spoke about the Arboretum’s decision to pilot the use of goats. The group met on Wednesday, September 21 at 6:00pm at Acc. # 683-84*A, Fraxinus pennsylvanica var. subintegerrima, a short walk from the Poplar Street Gate on the east end of Bussey Street at the edge of Peters Hill.

TreeMob™! Saving Monarch Butterflies

August 2016

Jose Luis Alvarez is a Mexican tree nurseryman, who for decades has been growing trees for reforestation projects. In 1997, he created Forests For Monarchs (FFM) also known as La Cruz Habitat Protection Program (LCHPP), an innovative non-profit designed to restore monarch butterfly (Danaus plexippus) forest habitat in Mexico and at the same time give indigenous people a desperately needed source of wood for cooking, heating and building houses. Alvarez will discuss monarch evolution, migration and population changes. He will also review the science which led to the discovery of over-wintering grounds in Mexico and the effort to reforest them. Alvarez will also address monarch habitat issues in the United States, and the work being done to stabilize the monarch population. Meet at the Dawn Redwood (Acc. # 524-48*Z), close to the intersection of Valley Rd and Hemlock Hill Rd on Sunday, August 28 at 1:00pm. Suggested parking: Bussey Street.

TreeMob™! Rockery Revelations

August 2016

The Arboretum’s 2016 Isabella Welles Hunnewell Interns just completed their group project, an annual requirement for our horticultural training program. This year’s project focused on the outcrops of puddingstone along Valley Road known as the Rockery. Their assignment was to propose development of this area with clear direction for collections expansion, horticultural management, and aesthetic improvements. They created a vision and mission for the space as both an area with unique growing conditions for showcasing scree-loving plants and a compelling destination for visitors. Join several of the interns at the Rockery to learn about their proposal and what they discovered as they researched the history of the site, tapped Sargent’s vision, and considered the list of plants targeted to expand the living collections of the Arboretum as part of the Campaign for the Living Collections. Meet at Acc. # 16865*D, dwarf chestnut oak (Quercus prinoides), on Thursday, August 11 at 3:00pm.

TreeMob™! Atmospheric Nitrogen Pollution in Urban Ecosystems

July 2016

Nitrogen emissions from electrical power plants, automobile exhaust and fertilizer applications are the major sources of nitrogen deposition in rain and snow onto ecosystems of the northeastern United States. Small amounts of nitrogen deposition can serve as fertilizer and stimulate productivity of plants. However, high rates of atmospheric deposition can lead to a series of negative consequences, including reductions in plant diversity, acidification of soils and waterways, and negative effects on human health. Boston University Associate Professors Pamela Templer and Lucy Hutyra established an atmospheric deposition monitoring site at the Arnold Arboretum earlier this year to measure and monitor rates of atmospheric deposition throughout the year in the City of Boston. This site is now part of the national network of deposition sites, known as the National Atmospheric Deposition Program (NADP), made possible through a grant from the DaRin Butz Foundation. The group learned what their research reveals about nitrogen in the City of Boston. The group gathered at the top of Weld Hill, behind the Weld Hill Research Building at 3:30pm on Tuesday, July 26, 2016.

TreeMob™! Pollinators Present

July 2016

Pollinators are necessary for around 1/3 of the food that humans eat. Over 300,000 species of plants rely on animals for pollination services. Pollinators come in many sizes and shapes — birds, bats, moths, butterflies, flies, and of course, bees. During this tree mob with researcher Callin Switzer, who studies interactions between plants and pollinators, we looked for and identified a variety of common pollinators (mostly bees) found in the Arnold Arboretum. The group gathered at 6:00pm on Wednesday, July 20, in the Leventritt Garden at Acc. # 104-2007*E, oakleaf hydrangea (Hydrangea quercifolia), with Callin Switzer from the Hopkins Lab at the Arboretum and his guest, Avery Russell, another bee scientist and graduate student in the Papaj Lab at the University of Arizona.

TreeMob™! Enigmatic Acer cappadocicum

July 2016

Acer cappadocicum ‘Aureum’ (Acc. # 442-36*B), with its blond canopy rising above others in the maple collection, catches your eye as you stroll down Bussey Hill Road and look across the rosaceous collection. This curious tree, a cultivar of Coliseum Maple accessioned in 1936, has been experiencing rather dramatic summer leaf bleaching for the past several years, with many leaves in the upper canopy turning stark white and dropping from the tree. Multiple causes have been hypothesized, from a somatic mutation in part of the crown to innate susceptibility of the cultivar due to insufficient photo-protective pigments. Putnam fellow Chase Mason explained results of a phytochemical investigation of potential causes of this phenomenon. To appreciate the canopy from across the rosaceous collection, the group gathered by Carefree Beauty™ Rose (Acc. # 407-97*MASS) at the intersection of Forest Hills, Bussey Hill, and Meadow Roads on Thursday, July 14, 2016 at 6:00pm.

TreeMob™! Endless Watermelons

June 2016

Endless watermelons, cantaloupes, cucumbers, and zucchini are ubiquitous signs of an American summer. How did that happen? Most of the foods in our diet, including the aforementioned summer staples, are recently introduced species that are not native to the Americas. In this Tree Mob, we considered the geographic and evolutionary origins of our favorite food plants and the changes that occur in certain plant traits during the process of plant domestication. Then, we discussed what the recent human-mediated movement of so many species of plants around the world means in an ecological context. The group met with Lori Shapiro of the Pierce Lab at Harvard University in the Leventritt Shrub and Vine Garden at Acc. # 332-84*B, Vitis vinifera x amurensis ‘Beihong’ on Thursday, June 30 at 6:00pm.

TreeMob™! Tinkering with Tolerance in Azaleas

May 2016

Deciduous azaleas in North America are a valued group of ornamental plants, not only in the northeast where many are native, but in harsher climates such as the upper Midwest. To assist the development of cultivars suited to challenging environments, visiting researcher Alexander Susko is figuring out ways to use wild azalea populations for improving the stress tolerance of this group of flowering shrubs. Alex spoke about how we can draw useful inferences about stress tolerance in nature to guide the breeding of these beautiful plants. The group met on Meadow Road at Acc. # 3237*C, Rhododendron periclymenoides (Pinxterbloom azalea), accessioned in 1888, on Wednesday, May 25 at 6:00pm.

TreeMob™! Jack’s Lilacs

May 2016

Lilac season was off to a slow start with prolonged cool temperatures, but it edged toward peak bloom. “Lilac Jack” Alexander, the Arboretum’s propagator and lilac expert, visited the three lilac cultivars that he introduced. He began his story at one of the Arboretum’s oldest accessions, Syringa reticulata, the common Japanese tree lilac accessioned in 1876, and moved on to Syringa ‘Lilac Sunday’, ‘Purple Haze’, and ‘Foxey Lady’. (Yes, he’s a Hendrix fan.) The group met at Acc. # 1111*A, Syringa reticulata, on Bussey Hill Road on Tuesday, May 10 at 5:00pm.

TreeMob™! Tree Health and Safety

May 2016

It can be difficult to determine when a tree becomes a safety hazard, but there are telling signs that inform our arborists’ judgment in the care of the living collections. Head Arborist John DelRosso spoke about damage caused by recent storms and how his team gives their best effort to keep Arboretum trees as healthy and safe as possible. The group met at Acc. # 12560*C Acer saccharinum at 6:00pm on Tuesday, May 3 on Meadow Road.

TreeMob™! Cherries Galore

April 2016

The Arboretum’s collection of cherry trees includes some rare native species, some plants collected early on in E. H. Wilson’s career, and many not easily found in the nursery trade. Horticultural technologist Kit Ganshaw, who cares for plants in the Bradley Rosaceous Collection, showed off some gems in the genus Prunus. We gathered near the Forest Hills Gate where, in a small area, we were able to explore a diversity of unusual cherries in bloom. Meet at Acc. # 706-31*B Prunus cyclamina on Tuesday, April 19 at 3:00pm.

TreeMob™! Winter Moth

April 2016

Winter moths (Operophtera brumata) are now a scourge in eastern Massachusetts and beyond. You may have observed them crowding your lighted entryway on November and December nights. But before they become moths, the winter moth caterpillars wreak havoc as they eat their way through buds and leaves of trees and shrubs in springtime. Some of their favorite food sources are maples, oaks, apples, birches, and blueberries, which they can significantly defoliate. Arboretum horticulturist Rachel Brinkman spoke about her research to determine how winter moth hatch timing affects the amount of defoliation of a host tree. The group gathered at Malus orientalis, Acc. # 213-2001*A, on Wednesday, April 6 at 4:00pm.

TreeMob™! Spring Renewal at the Hunnewell Building

March 2016

The landscape gracing the front of the Hunnewell Building has undergone renovations and renewals over the past century. Each change has been intentional, relating selected plants to the Arboretum’s history. The last major renovation took place in 1993 when both the building and the landscape underwent a major overhaul. To incorporate an accessibility ramp to the front doors, a berm was created and a planting design per former staff members Stephen Spongberg and Peter Del Tredici was installed. In March 2016, twenty-three years later, the Arboretum’s curation team and horticulturists are revamping once again. Crew members Jed Romanowiz and Greg LaPlume spoke about the reasons for replanting and the other changes they are making to the Hunnewell Building landscape, all in the name of improvement. The group gathered at the front of the Hunnewell Building at 3:00pm on Tuesday, March 24.


TreeMob™! Synchronous Flowering and Fruiting: Franklinia alatamah

October 2015

Synchronous flowering and fruiting is a rare phenomenon in deciduous trees, but is evident in Franklinia alatamaha. Kristel Schoonderwoerd, a Graduate Student in the Friedman Lab at the Arboretum, spoke about her research into the reproductive mysteries of the Franklin tree. The group met at Acc. # 2428-3*B on Bussey Hill in the Explorers Garden on Tuesday, October 27 at 3:45pm.

TreeMob™! Pinus ponderosa: Icon of the West

October 2015

Charles Sargent’s favorite pine was Pinus ponderosa. As he described it in the Silva of North America, it is “an emblem of strength, it appears as enduring as the rocks, above which it raises its noble shafts and stately crowns.” His good friend John Muir begged to differ. Ponderosa pine is the most widely distributed pine species in North America. It thrives throughout the western United States and has five regionally based subspecies adapted to divergent growing conditions. Over the eons, fire has been essential part of the ponderosa forest life. Of the 18 trees planted at the Arnold Arboretum, the oldest was accessioned in 1902. The group gathered at this tree (Acc. # 16457*E) on Monday, October 19 at 3:00pm with mob leader Maggie Redfern, Assistant Director, Connecticut College Arboretum.

TreeMob™! Prepping for Propagation

October 2015

Collecting, storing, and triggering seeds to germinate is a tricky business. It requires patience, skill, and knowledge. It also requires an understanding of the various means of seed dispersal and the environments and processes that allow seeds to sprout in their native habitat. Mimicking nature is the key to success. In this tree mob, Propagator Jack Alexander and Manager of Plant Production Tiffany Enzenbacher showed some of the fruits, nuts, and seeds that are in line to become a new generation of Arboretum plants and spoke about the treatments that various seeds undergo to trick them into sprouting. The group met inside the Dana Greenhouses on Wednesday, October 14 at 1:00pm.

TreeMob™! Seeds, Glorious Seeds

October 2015

Arboretum educators Ana Maria Caballero and Nancy Sableski alongside Boston Public School teachers launched a variety of winged seeds from the arborists’ bucket truck to see which seed structures were most aerodynamic, compare surface area in relation to flight success, and even make some bets on farthest dispersal. After the seed drop, tree mob participants helped gather data from the seed landing grid. The group met near Acc. # 147-2000*A (Liriodendron tulipifera x chinense) on the Hunnewell Building lawn on Saturday, October 3 at 10:00am.

TreeMob™! Crazy for Corylus

September 2015

Arboretum Gardener Robert Dowell has a fondness for filberts and wonders why they aren’t more commonly grown in Massachusetts. Robert presented an overview of the Arboretum’s Corylus sp. collection including species from the US, Europe, Japan, China, and the Republic of Korea. The group met on September 8 at Corylus americana, Acc. # 1229*A, and visited several specimens in the Bradley Rosaceous Collection.

TreeMob™! Maple Diversity

August 2015

Jianhua Li, PhD, former research scientist at the Arnold Arboretum and now Associate Professor of Biology at Hope College in Holland, Michigan, spoke about his research that is helping to define natural groups within the maples and trace the evolutionary pathways of important features, such as fall foliage, gene duplication and chromosome doubling in some maple species, as well as identifying cultivar parentage. The group met at Acc. #213-91*AAcc. # 213-91*A on August 19 at 6:00pm to learn about similarities and differences among the maples.

TreeMob™! What’s Soil Got to Do with It?

August 2015

Soil is the medium in which all of the Arboretum’s trees shrubs and vines grow. However, we don’t have comprehensive, up-to-date data about the composition of this soil as it varies across 281 acres. This summer, the Isabella Welles Hunnewell Interns focused their project on soil health assessment, historical soil data analysis, and the development of a soils management plan for the Arnold Arboretum. The Tree Mob gathered under the shade of a shellbark hickory, Carya laciniosa, Acc. # 12898*J, at 2:00pm on Monday, August 10 to learn how 9 interns tackled this undertaking, what they discovered in the process, and their recommendations for short- and long-term improvements for the health of the living collections.

TreeMob™! When the Invasive Gets Tough…Make Beer?

July 2015

Fallopia japonica, also known as Japanese knotweed, fleeceflower, Mexican bamboo, and other common names, is a highly successful, non-native perennial from eastern Asia. It can be seen along roadsides, riverbeds, and in empty lots in impenetrable stands up to 10 feet in height. It is indeed tough. But in the early spring, it is also tender…and edible. Pamela Thompson, Arnold Arboretum Manager of Adult Education, was joined by local wild edible enthusiast Pamela Kristan, Boston area beer enthusiast and conservationist Kristen Sykes, and brew master for the Cambridge Brewing Company Will Meyers, to share the history of this plant’s movement around the globe and the gustatory possibilities of this pernicious perennial, including beer. The group gathered on Hemlock Hill Road, near Acc. # 1126-68*A (Kalmia latifolia ‘Polypetala’), on Wednesday, July 29 at 6:00pm.

TreeMob™! Genetic Giant: Sequoiadendron giganteum

July 2015

The giant sequoia (Sequoiadendron giganteum) is the largest tree species on earth. Yosemite National Park’s Mariposa Grove in California has approximately 500 mature sequoias today. The oldest specimens there are over 3,000 years old. The Arnold Arboretum currently has six giant sequoias in its collection. The group gathered by the largest specimen, <a href=”(Acc. # 1320-72*A, which stands at roughly 60 feet in height and has a diameter of over 55 inches and was transplanted to the Arboretum when it was 42-ft tall. Manager of Horticulture Andrew Gapinski and Curator of Living Collections Michael Dosmann spoke about the challenges faced by this western species growing in New England and the effects of a changing climate on the longevity of this particular specimen. The group met at 6:00pm on Thursday, July 23 in the conifer collection.

TreeMob™! Citizen Science Advances Research

July 2015

Citizen science is transforming research in the environmental sciences. Lizzie Wolkovich, PhD, Assistant Professor, Organismic and Evolutionary Biology at Harvard University, and Ailene Ettinger, PhD, Putnam Fellow, both resident researchers at the Arnold Arboretum, explained the concept of citizen science, provided some examples of research programs that are using this populace-powered method of data collection, and discussed opportunities to participate via the Arboretum’s Tree Spotters program. The group met at Acc. #1323-82*A Tilia americana, American basswood, on Peters Hill at 1:00pm on Tuesday, July 21.

TreeMob™! Stipules and Bonus Mob on Birches in Full Fruit

July 2015

Arboretum Director and Arnold Professor of Organismic and Evolutionary Biology William (Ned) Friedman focused on the Arnold Arboretum’s outstanding birch collection on Bussey Hill, shedding light on one of the largely unappreciated parts of the leaf, the stipule. This amazing leaf specialization helps ease this transition to adulthood for the leaves of many diverse plant species, including birches. He additionally discussed birch fruit. The group gathered at Betula grossa, Acc. # 199-2007*A at 7:00pm on Friday, July 10, 2015.

TreeMob™! Costs and Benefits of Flowering First

July 2015

Some plants, including some dogwoods, magnolias, and redbuds, among others, flower in the spring before they leaf out. Such precocious blooms tap a plant’s resources when it is perhaps least able to supply needed carbon and water. Jessica Savage, PhD, a Putnam Fellow at the Arnold Arboretum, is conducting research to examine carbon transport in plants in conjunction with flowering phenology to better understand why plants bloom when they do. The group gathered on Thursday, July 9 at 6:00pm at Acc. # 1916-80*A (Cornus kousa) to hear about Jessica’s research questions and techniques she’s applying in the Arboretum’s living collection to compare species with pre- and post-leaf out flowering strategies.

TreeMob™! Culture, Collections, and the All-too-comfortable Guest

July 2015

An intractable weed unleashed from its native forests in China, Ailanthus altissima, the Tree of Heaven, is perhaps the epitome of the invasive urban tree. Often maligned, what would it mean to reexamine our relationship with this once-invited, now-despised plant? As a splendid specimen in the Arboretum, a flourishing wild population in Bussey Brook Meadow, and in feral profusion at the edges of the Arboretum and the city beyond, Ailanthus is as provocative as it is successful. Matthew Battles, associate director of metaLAB at Harvard and Kyle Parry, a recent doctoral recipient from Harvard’s Department of Visual and Environmental Studies, delved into the history and presence of this ubiquitous urban “bad boy” as they pondered culture and collections. The group met in Bussey Brook Meadow.

TreeMob™! Mixing It Up in the Rosaceae

June 2015

Jonathan Mahoney, a researcher at the University of Connecticut, investigates intergeneric plants. At the Arnold Arboretum, he is specifically studying the intergenerics × Sorbaronia and × Sorbopyrus along with their parent genera Aronia, Sorbus, and Pyrus. Jon spoke about these plants that are not “faithful” to genus, as most plants are, but instead are able to interbreed with other genera in the same family. The group gathered in the Bradley Rosaceous Collection at Acc. # 759-78*C.

TreeMob™! Charcoal Tales

May 2015

Paleoethnotbotanist John (Mac) Marston, PhD, explained how archaeologists use small fragments of ancient, burned wood to understand environmental change and described some of the results from his collaborative work in central Turkey that show long-term human impacts on forests. The group gathered in the Conifer Collection at 6pm on Thursday, May 21 at Juniperus excelsa Acc. # 17-2003*C.

TreeMob™! Expanding the Collection on Arbor Day

April 2015

Staff and visitors gathered on April 24 as we added Magnolia stellata (Acc. # 393-2008*B) to the collection of magnolias that adorn the Hunnewell Lawn. Andrew Gapinski discussed the provenance of this plant and proper care for a newly planted specimen. Jordan Wood fastened on the official identification tag to this specimen that we hope thrives for a century or more.

TreeMob™! Repotting Bertha

April 2015

Bonsai specialist Glenn Lord repotted one of the oldest and largest dwarf potted plants in the Larz Anderson Bonsai Collection. Bertha, as she is fondly called, was started in 1787 as a seedling in Japan. She was purchased from the Yokohama Nursery Company by the Honorable Larz Anderson and brought to his Brookline Estate in 1913. A Chamaecyparis obtusa ‘Chabo-hiba’ or compact hinoki cypress, Bertha moved a few miles east to the Arnold Arboretum in 1949. Bertha (Acc. # 892-49*A) from her original pot into a new one. The group met in the Leventritt Shrub and Vine Garden to watch the repotting of this 228 year old specimen.

TreeMob™! Tough Decisions Make a Fine Collection

April 2015

Removing a tree from this public arboretum can trigger a variety of questions and emotions, from visitors and staff alike. Acc. # 661-70*B, Stewartia pseudocamillia, situated next to the walkway to the Hunnewell Building, was removed. The decision, though considered with great thought, was not difficult to make for Curator of Living Collections Michael Dosmann and Manager of Horticulture Andrew Gapinski. A host of criteria and data are considered when adding to, as well as subtracting from, the living collections of the Arboretum. The group met to learn about the remedial care provided to this Japanese stewartia over the years, the importance of provenance when assessing a collection, and the steps taken in the de-accessioning process.

TreeMob™! Repotting Bertha

January 2015

Horticultural technologists Rachel Brinkman and Sue Pfeiffer demonstrated how we monitor moth populations, what we find, and how we use this information to guide the care of the living collections. The group met in the Hunnewell Building Lecture Hall.


TreeMob™! When a Tree Falls…

October 2014

During last week’s nor’easter, a large pin oak (Quercus palustris) fell, and we’re sure it made a sound. We believe this enormous tree predates the 1872 creation of the Arnold Arboretum, but since it was not tracked as a part of the collection until 1950, we don’t know how old it actually is. Join Arboretum Putnam Fellow Ailene Ettinger as we core this beauty of a specimen in hopes of determining its approximate age. The group gathered at Acc. # 22893*E.

TreeMob™! Yellow on Yellow: American Witch Hazel

October 2014

American witch hazel (Hamamelis virginiana) is an understory shrub that begins to flower in autumn and continues into December. Producing a subtle scent that wafts on the breeze, it has long petals that unfurl, creating asterisk-like flowers in pale yellow. The foliage at this time of year is changing from deep green to brilliant yellow. Andrew Gapinski spoke about this North American native and other witch hazels of merit. The group gathered at Acc. # 22947*B.

TreeMob™! North American newbie: Heptacodium miconioides

October 2014

The story of Heptacodium miconioides, or the seven-son flower, illuminates the trajectory of an exotic plant from discovery to propagation, to distribution and observation, and finally to the point at which it enters the nursery trade. Native to high cliffs in the western Hubei province of China, seven-son flower is rare in the wild. This large, arching shrub with exfoliating bark is covered with pale white flowers in late summer, but is most resplendent in the autumn when its calyces and fruits turn rose-purple. Maggie Redfern, Visitor Education Assistant, brought to light the role of the Arnold Arboretum and other botanical gardens in this plant’s debut in North American horticulture. The group met at Acc. # 1549-80*H.

TreeMob™! Mushrooms of the Arboretum

October 2014

Rosanne Healy, a post-doctoral fellow in the Pfister Lab at Harvard, identified some of the fungi that are fruiting and discussed their role in keeping the Arboretum healthy (or in some cases, not so healthy!). She spoke about fungi that are in mutually beneficial partnership with tree roots, fungi that are involved in recycling of dead wood, and fungi that are parasites on some tree species. The group met on Hemlock Hill at Acc. # 1350-98*A.

TreeMob™! First Blush

September 2014

Acer rubrum ‘Schlesingeri’ is a beacon opposite the Hunnewell Visitor Center entrance, signaling the coming autumn as one of the first maples to color the landscape. Michael Dosmann, Curator of Living Collections, spoke about the mechanics of leaf-color change and the local provenance of this venerable and colorful cultivar. The group met opposite the Visitor Center at Acc. # 3256*A.

TreeMob™! Building with Bamboo

September 2014

Engineers at the Massachusetts Institute of Technology are studying the mechanical properties of bamboo, with a view towards developing structural bamboo products, analogous to wood products such as plywood, oriented strand board, and glue-laminated wood. Bamboo is renewable, is widespread in countries with rapidly developing economies (such as China, India and Brazil), and grows remarkably quickly. Lorna Gibson, Professor of Materials Science and Engineering at MIT, will discussed how bamboo grows, what its interior structure looks like, and how it can be used in structural bamboo products. The group met at the bamboo grove, at Acc. # 369-80*MASS, (Phyllostachys bambusoides).

TreeMob™! Flower Power: Reproductive Isolation

September 2014

Reproductive isolation is essential for maintaining species identity. Most flowering plants prevent fertilization by their own pollen to impede inbreeding, and also block fertilization by pollen from different species to avoid hybridization. Federico Roda, a post-doctoral fellow in the Hopkins Lab, used clovers to explain how flowers detect and reject undesired pollen. The group met at the top of Weld Hill.

TreeMob™! The Big Reveal: 2014 Hunnewell Internship Group Project

August 2014

What do you get when you present a landscape challenge to a group of young, intelligent, and creative horticulturists? In the case of this summer’s “group project” assigned to the Isabella Welles Hunnewell Interns, the result is a phenomenal new outdoor space for staff use and enjoyment. Though our interns typically develop a project to improve or revitalize a public area of the Arboretum, this year’s challenge took place behind the scenery. With a small budget and tight timeframe, the interns combined their backgrounds in arboriculture, horticulture, ecology, plant science, and landscape architecture to complete a major landscape renovation and reconstruction of the Hunnewell Building staff patio garden. Hunnewell Interns Chris Copeland, Olivia Fragale, Robert Dowell, and Kassie Urban-Mead gave an overview of their design-build process and toasted the end of summer for a project well done. The group met at the service gate located to the right of the Hunnewell Building.

TreeMob™! How to Tolerate your Family: Lessons All Can Learn from Willows

August 2014

Due to competition for water and resources, it is uncommon for closely related species to grow together in the same location. However, willows (Salix sp.) defy this pattern and appear content to grow alongside other members of their family. Jessica Savage, a newly appointed Putnam Fellow at the Arnold Arboretum, explained why and how willows maintain their high diversity while living in close quarters with relatives and sharing “one bath.” The group met at Acc. # 172-97*A, Salix schwerinii.

TreeMob™! Pinus strobus—The Framework of New England

August 2014

New Englanders who pay any attention to trees probably know a bit about white pine, Pinus strobus. Though not a native New Englander herself, Arboretum Curatorial Assistant Irina Kadis knows this species exceedingly well. Irina spends her free time exploring eastern Massachusetts, cataloging and describing the state’s native flora in its forests, meadows, barrens, and bogs. The group heard about white pine lore and botanical facts about an iconic species which fueled the growth of the colonies and continues to be an important natural resource today. The group met at Acc. # 875-2008*A at the northwestern base of Peters Hill.

TreeMob™! Ashes to ashes…

August 2014

On July 16, a single adult emerald ash borer (EAB) was spotted during a routine check of monitoring traps deployed in the Arnold Arboretum landscape as part of a cooperative detection effort with the Massachusetts Department of Conservation and Recreation (DCR). Manager of Horticulture Andrew Gapinski and Curator of Living Collections Michael Dosmann spoke about the Arboretum’s ash (Fraxinus) collection with species from North America, Asia, and Europe; how the collection will be managed in the presence of EAB; and explained how to identify this iridescent green beetle and its telltale signs of damage. The group gathered in the ash collection at Acc. # 7033*F, Fraxinus tomentosa.

TreeMob™! Über Intriguing Virginia Roundleaf Birch

July 2014

Richard Nixon. Wint O Green® Life Savers®. Questionable identities. These are just part of the interesting story behind Virginia roundleaf birch (Betula uber), a rare tree species that was once near extinction and remains threatened in the wild. Arnoldia editor Nancy Rose met the group in the Arboretum’s birch collection on Bussey Hill at Acc. # 1433-84*A.

TreeMob™! What’s the buzz? Tell me what’s a-happening…

July 2014

A plant’s flower shape and anther structure determine the type of pollinator needed and how successful pollination will be. Bees, responsible for pollination of many of the food crops we eat, seek out flowers to drink nectar or gather pollen. Last summer, Harvard University graduate student Callin Switzer closely observed and actually recorded buzzing frequencies of a variety of bee species at the Arboretum. Callin’s Tree Mob at Acc. # 287-96*A offered visitors a closer look at bees and the flowers they visit, including ways that plants have evolved to “serve” their pollen to the bees, how bees have evolved alongside flowers to meet their own nutrient needs, and the amazing physiology of buzzing.

TreeMob™! The Snow Queen of Summer

July 2014

Come July, many ornamental trees and shrubs have flowered and are putting their energy into seed development. Not so for oak leaf hydrangeas. The heat hits and they send forth showy panicles of creamy white contrasted against textured, deep green leaves. Hydrangea quercifolia ‘Snow Queen’ ranks high on Supervisor of Horticulture Andrew Gapinski’s list of favorite shrubs. The group met at Acc. # 318-94*A.

reeMob™! It’s chilly out there…for the Mountain Hemlock

July 2014

Mountain hemlock (Tsuga mertensiana) is native to mountains of the western US, where it can be covered in snow for up to 10 months of the year. It’s hard to imagine now that summer is finally here in New England, but much of mountain hemlock’s native habitat won’t be free of snow until mid-July or later! Putnam Fellow Ailene Ettinger spoke about this species’ adaptations to cold environments, how it may be affected by climate change in the future, and how research like hers, conducted in natural habitats and among the collections at the Arnold Arboretum can help us understand how this and other tree species might adapt to climate in flux. The group met at Acc. # 693-77*A.

TreeMob™! Clematis: What a Plant Will Do for Love

June 2014

The beauty of clematis may trick you into believing that these spectacular and bizarre flowers were bred to ornament your lampposts and trellises, but in fact, they evolved to attract bees. There are over 300 species of clematis that display incredible natural diversity of flower shape, color, and smell. This explosion of diversity attracts bee pollinators from the tropics to the sub-arctic. The seemingly endless malleability of form and color has enabled the creation of hundreds of cultivated varieties that now accent yards around the world. The Arnold Arboretum holds an exemplary collection of both natural species and cultivated forms of clematis. The group met at the heart of this collection in the Leventritt Shrub and Vine Garden at Acc. # 372-2003, Clematis viticella ‘Betty Corning’, and heard from Harvard Assistant Professor of Organismic and Evolutionary Biology Robin Hopkins about form, color, and the science of attraction.

TreeMob™! Clematis: An American All-star: Yellowwood

June 2014

As one of the seldom-planted but more beautiful flowering trees native to North America, yellowwood, Cladrastis kentukea, deserves attention. Taking up to 20 years to first flower and only producing good shows every two-to-three years, it is a tree for the patient and committed gardener. Curatorial Fellow Jordan Wood spoke about its discovery by André Michaux in 1796 and the Carolina expeditions of Michaux and his son François André. The group met at Acc. # 13055*B, a broadly spreading specimen accessioned into the Arboretum’s collections in 1881.

TreeMob™! You say Catalpa, I say Catawba!

June 2014

The Arnold Arboretum’s catalpa collection holds 39 accessions, representing two species native to North America (Catalpa bignonioides and C. speciosa), three species that hail from China (C. ovata, C. bungei, and C. fargesii), and some cultivars. Often referred to as bean trees for their 6- to 16-inch slender fruits, they reveal their glory in June with clusters of sweetly scented flowers. Arboretum Director William (Ned) Friedman spoke about the catalpa collection and intercontinental (eastern Asia/eastern North America) disjunct species, so characteristic of many of the fine collections at the Arnold Arboretum. The group met at Acc. # 17664*A, Catalpa fargesii, a rarity in its native habitat and in horticulture.

TreeMob™! Nantucket Shadbush

June 2014

Each year the many species of Amelanchier bring dramatic floral displays to New England in May and June. Amelanchier nantucketensis, the Nantucket shadbush, serves as a fascinating study in the interplay of natural hybridization, conservation, plant reproduction, and land use in New England. Arboretum scientist Dave Des Marais discussed the role that the Arboretum plays in preserving rare species, and how Amelanchier nantucketensis is serving as a valuable tool to understand the genetics and ecology of natural populations. The group met at the centerpiece of our amelanchier collection, Acc. # 934-89*A.

TreeMob™! Malicious Men May Die, but [Malus] Never.

May 2014

I’ve toyed with Moliere’s quote about malice from Tartuffe in this Tree Mob’s title, however there may be some truth to my version. Apples (Malus), thought to have originated in central Asia, have been around for upwards of 7 million years. Visiting researcher and recipient of the Jewett Prize, Ling Guo, is a horticulturist, professor, and curator in the Department of Plant Introductions at the Beijing Botanical Garden. Ling has spent several months studying the Arnold Arboretum’s crabapple collection on Peters Hill and talked about her research. The group met at Acc. # 1645-52*A, Malus x arnoldiana.

TreeMob™! Distinctively Deciduous Conifers

May 2014

Deciduous gymnosperms that used to dominate vast areas of the earth in ancient times went through a dramatic reduction in species richness and ecological dominance due to climate change and competition from angiosperms. Now, extant conifers are overwhelmingly evergreen. Metasequoia glyptostroboides is one of the few representatives of the extant conifers with deciduous leaf habit. For this tree mob, Putnam Research Fellow Guang-You Hao talked about the ecology of deciduous conifers, which may provide clues to their extinction and habitat shrinkage as well as their persistence under certain conditions. The group met at Acc. # 524-48*Z.

TreeMob™! Winged but Rooted: American Sweet Gum

May 2014

Arnold Arboretum Director William (Ned) Friedman considered the form and function of winged bark of American sweet gum (Liquidambar styraciflua Acc. # 1248-79*B).

TreeMob™! It’s a Tree. It’s a Shrub. It’s Alnus!

April 2014

The flower catkins paired with the pine-like pseudocones of the genus Alnus are a charm in the late winter and early spring months in Boston. The Arnold Arboretum’s diverse collection of Alnus showcases the variability of species from East Asia to Europe, and locally within Massachusetts. In this Tree/Shrub Mob, Curatorial Fellow Joyce Chery highlighted the world distribution, ecology, and lifecycle of this fascinating group—cousins to the birches—as well as some associated taxonomic horrors. The group met along Willow Path, where most of the Arboretum’s Alnus collection is situated, at Acc. # 125-2005*B, Alnus incana ssp. rugosa.

TreeMob™! Conjuring Spring with Hamamelis vernalis

March 2014

In New England, it is a bit magical to see a plant flowering through the dead of winter and on into spring. Such is the beauty of Hamamelis vernalis, typically in bloom from January to March, allowing us to say, “There’s always something in bloom at the Arboretum.” Visitor Educator Maggie Redfern spoke about the horticultural history of the type specimen of Ozark witch hazel. The group met beside Rehder Pond at Acc. # 6099*D.


TreeMob™! Sargent’s Weeping Hemlock

December 2013

Contradictions, lost or unrecorded facts, and misstatements attributed to Sargent’s Weeping Hemlock (Tsuga canadensis f. pendula) shroud the plant’s origins in mystery. Senior Research Scientist Peter Del Tredici illuminated what has been discovered about this plant by digging into historical records, speculating about locations, and in some cases, taking core samples to count rings. The group met at Acc. # 1514-2*A, a sculptural beauty, on Hemlock Hill Road.

TreeMob™! Techno Mob: Archaeological Mapping

November 2013

Professors and students of Boston University’s Department of Archaeology are spending a few days this fall semester at the Arnold Arboretum to study the remains of historic archaeological sites. The team is using a variety of surveying equipment and geophysical instruments to map remains both on and below the ground surface. Professor Chris Roosevelt and his students met at the site of the former Bussey Mansion to learn about techniques used today to map and interpret what remains on the land. The group met on Beech Path at Acc. # 655-93*A, sugar maple (Acer saccharum).

TreeMob™! Seduction and Dispersal: Euonymus Species

November 2013

Arnoldia editor Nancy Rose spoke about seed dispersal in general and specifically about the fruiting structure of euonymus species. Nancy showcased some of the species in the Arboretum’s collection and compared native and non-native characteristics and discussed issues of invasiveness. The group met on Bussey Hill Road near its intersection with Valley Road at Acc. # 1518-83*A, Euonymus europaeus.

TreeMob™! The Bitter and the Sweet of Vines

October 2013

Research conducted by Putnam Fellow Stacey Young in the collections is flagged by blue tape that you may have noticed as you wander the Leventritt Shrub and Vine Garden. There, and elsewhere in the landscape, Stacey is examining biological, morphological, and ecological traits of both North American and Asian temperate lianas (woody vines). Come learn about the ecology of invasiveness and decline within the bittersweet genus, and in general, consider how vines climb. The group met in the Shrub and Vine Garden at Acc. # 269-95*A, anglestem bittersweet (Celastrus angulatus), a non-invasive (we believe) Asian relative of the highly invasive oriental bittersweet (Celastrus orbiculatus).

TreeMob™! Actinidia polygama: The Next Superfood?

October 2013

Rachel Brinkman, Horticulture Apprentice, has been keeping an eye on the various hardy kiwi vines (Actinidia sp.) in the Leventritt Garden, which displays seven different species. She will speak about Actinidia polygama, silver vine, whose fruit might be ripe for sampling. The group met in the Leventritt Garden at Acc. # 460-83*B and learned about this demure but vitamin-rich relative of the kiwifruit commonly found in grocery stores.

TreeMob™! Landscape with Edibles: Prunus maritima

September 2013

Kristina Jones, Director of the Botanic Gardens and faculty member in Biology and Environmental Studies at Wellesley College, spoke about beach plum, Prunus maritima. Interested in ecological approaches to growing food such as edible forest gardens, and partnering with permaculture experts to analyze productivity and sustainability of designed edible ecosystems, she spoke about the food value and horticultural uses of this stone fruit native to the eastern seaboard from New Brunswick to Virginia. The group met at Prunus maritima forma flava, Acc. # 262-92*C on Peters Hill.

TreeMob™! A Landscape Transformed

September 2013

In recent years we have assigned a group project to our Hunnewell Horticultural Interns as culmination of their experience in the Arboretum’s landscape. This year’s interns concentrated on an area just below the Explorers Garden, along Oak Path. Intern Joe Leonard spoke about the group’s design and process for transforming a once unwelcoming and challenging-to-manage area of the Arboretum. The group met on Oak Path near its intersection with Beech Path.

TreeMob™! Cattail Leaves

August 2013

Cattail leaves stand nearly vertical and can be up to 6 feet tall. How do they do it? Professor Lorna Gibson from the MIT Cellular Solids Group spoke about the sandwich structures within these reeds that provide stiffness and strength and explained how such structures work in both plants and engineering. The group met along Meadow Road at the edge of the meadow.

TreeMob™! The Seaside Alder

August 2013

Alnus maritima, the seaside alder, is a bit of rarity, and our specimen of this plant is truly unspectacular. However, its story is intriguing. Endemic to the United States, it is found in three populations, remnants from a time when the plant was perhaps more widespread. Matt Jones, a 2013 horticultural intern at the Arboretum with an International Master’s in Horticultural Science and a Master of Science in Botany from the University of Oklahoma, spoke about this member of the Betulaceae. The group met at Acc. # 1217-4*A.

TreeMob™! Pawpaw

August 2013

Get to know the oft forgotten pawpaw, Asimina triloba, with the largest edible fruit native to North America. It is the only species of the Annonaceae (a tropical family that includes cherimoya, guanabana, and soursop) that is hardy in New England. Research associate Iñaki Hormaza, visiting from Spain, spoke about this humidity-loving small tree. Meet at Acc. # 205-91*A along Peters Hill Road.

TreeMob™! Dragonflies

August 2013

Dragonflies had wingspans of 60 centimeters 300 million years ago. Today, they are some of nature’s most accomplished fliers, spinning and flipping as they catch mosquitoes, flies, spiders, and more. This Insect Mob focused on dragonflies, their life cycle, flight patterns, and vital ecological importance. Led by Mary Salcedo, Harvard University Graduate Student in Organismic and Evolutionary Biology, the group met at Rosa virginiana, Acc. # 106-2006*A.

TreeMob™! Aesculus glabra var. glabra

August 2013

Maggie Redfern spoke about Aesculus glabra var. glabra, one of the Arboretum’s oldest accessions. She also discussed the history of the Arboretum’s South Street Gate. The group met at Acc. #: 262*A.

TreeMob™! Eastern Cicada Killers

August 2013

Straying from our woody plant theme this week, we learned about the Arnold Arboretum’s resident population of Eastern cicada killers, Sphecius speciosus. Birder, photographer, and volunteer Bob Mayer spoke about the life cycle and habits of this native insect on Forest Hills Road near the weeping cherries, east of Dawson Pond, at Acc. #: 290-87*A, Prunus subhirtella ‘Pendula’.

TreeMob™! Clethras: Sweet Scents of Summer

August 2013

The group met in the Leventritt Shrub and Vine Collection for a comparison of Clethra species, both native and exotic, and their cultivars. Propagator Jack Alexander spoke about habitat, floral characteristics, and what he would look for in the quest to find the ideal summersweet shrub in the wild. The group met at Acc. #: 287-96*A.

TreeMob™! Lime or Linden: Tilia cordata

July 2013

Michael Dosmann, Curator of Living Collections, told the story of a cultivar of Tilia cordata, collected by dendrologist and longtime Arboretum staff member Alfred Rehder, whose birthday was 150 years ago this year. The group met at the summit of Peters Hill at Acc. #: 12112*A.

TreeMob™! Tree of Heaven

July 2013

Senior Research Scientist Peter Del Tredici spoke about Ailanthus altissima f. erythrocarpa, a form of the Tree of Heaven. The group met at Acc. #: 695-80*B, to hear the story of collecting this plant.

TreeMob™! Taxus Tales

July 2013

Conifer aficionado Dennis Collins, Horticultural Curator at Mount Auburn Cemetery, talked about some of the reasons why Taxus, a genus of long-lived conifers, have captivated humans for religious, military, medicinal and horticultural reasons over the past few thousand years. The group met at Acc. #: 169-99*B, Taxus cuspidata.

TreeMob™! An Apple a Day…

July 2013

Juan Losada, Putnam Scholar and Postdoctoral Fellow in the Friedman Lab, mixed horticulture and history in speaking about the implications of apples in the human world. The group met at the top of the crabapple collection on Peters Hill by Malus sargentii, Acc. #: 93-96*B.

TreeMob™! Elements of Pruning

June 2013

Head Arborist John DelRosso discussed the reasons for pruning, what Arboretum arborists consider before making a cut, and how the age of a specimen informs their treatment. The group met at Acc. #: 496-2002*A, Acer davidii, located on Meadow Road opposite the cork trees.

TreeMob™! Plants and Climate Change

June 2013

Boston University professor Richard Primack used Pinus aristata, bristlecone pine, to illustrate the timing of leaf-out as related to climate change. Dr. Primack has been using Thoreau’s notebooks, Arnold Arboretum herbarium specimens, and other historical records to compare leafing and flowering times through the past century to the present. The group met in the dwarf conifer collection at Acc. #: 721-61*A.

TreeMob™! Mountain Laurel Mutant

June 2013

Arboretum Director Ned Friedman discussed the morphology of Kalmia latifolia ‘Polypetala’. One of the Arboretum’s older specimens, accessioned in 1885, this mountain laurel displays a rare inflorescence mutation. The group met on Hemlock Hill Road at Acc #: 2458*A.

TreeMob™! Chionanthus Here and There

June 2013

Nancy Rose spoke about disjunct species Chionanthus retusus and C. virginicus. These fringe trees are found on widely separated continents, one in Asia and the other in North America. She compared their similarities and differences, and considered how they have evolved and adapted in their disparate homes. The plants are located in the Explorers Garden on Bussey Hill at Acc. # 13051*A.

TreeMob™! Seeds and Seedlings

May 2013

How does a seed make it on its own, released from its parent plant to start anew? Sargent Fellow Sarah Mathews will speak about nurture and nature in germination and a plant’s strategy of abandoning its progeny to the ground. Meet at Acc. #: 19192*H.

TreeMob™! Japanese Azaleas: Rhododendron molle ssp. japonicum

May 2013

Join longtime Arboretum volunteer and rhododendron aficionado George Hibben to learn about the qualities of Japanese azaleas that endear them to hybridizers, with focus on the Arboretum’s Rhododendron molle ssp. japonicum. Meet at Acc. #: 28-98*A.

TreeMob™! Mutants in Our Midst

May 2013

Ever wonder how new horticultural forms and varieties come to be? For example, how does a green-leafed shrub morph into a gold-leafed variety, or a white-flowered plant develop from a species with magenta blooms? Join Ned Friedman, Director of the Arnold Arboretum, for the first of three mobs he will lead this spring exploring naturally occurring plant mutations that are the source of most of our horticultural wonders. Meet at Acc. #: 10-68*B, Cercis canadensis, commonly known as redbud.

TreeMob™! Pyrus pyrifolia, Sand Pear

May 2013

Senior Research Scientist Peter Del Tredici spoke about one of our older specimens, Pyrus pyrifolia, Acc. #: 7272*C. Native to China, Japan, and Korea, this plant was grown from seed that was collected in Hubei Province, China by E.H. Wilson in 1907. A standout in the Arboretum’s landscape, this plant has provided multi-season beauty on Bussey Hill for more than a century.

TreeMob™! Lilacs: Syringa oblata and Syringa x hyacinthiflora Hybrids

May 2013

Lilac season has begun with the earliest of the lilacs coming into full bloom. Plant propagator and lilac expert Jack Alexander introduced us to Syringa oblata and told the story of the creation of the first cultivar of Syringa × hyacinthiflora. Met in the lilac collection on the slope of Bussey Hill at Syringa oblata, Acc. #: 381-2001*A.

TreeMob™! Dwarf Sweet Box, Sarcococca humilis var. digyna

April 2013

Sue Pfeiffer, horticultural technologist, explained Sarcococca humilis var. digyna, Accession #: 667-2003*MASS a diminutive, sweet-scented evergreen groundcover, native to China. Sue will also discuss other members of the Buxaceae on display in the Leventritt Shrub and Vine Garden.

TreeMob™! Prunus mume, Chinese Plum or Japanese Apricot

April 2013

Along with bamboo and pines, the plant most intimately associated with art, literature, and everyday life in China is Prunus mume, Accession #: 233-2002*B, an early flowering plant in the Rosaceae; with Visitor Education Assistant Maggie Redfern.

TreeMob™! Jasminum nudiflorum, Winter Jasmine

April 2013

Brian Leib, manager of the Arboretum’s research greenhouses at the Weld Hill Building, spoke about this species from northern China in the Oleaceae. Grown as a ground-covering shrub or trained as a vine, winter jasmine’s yellow flowers signal the coming of spring. See a specimen in the Leventritt Shrub and Vine Garden at Accession #: 654-2003*A.

TreeMob™! Chimonanthus praecox, Winter Sweet

March 2013

Chimonanthus praecox, a member of the Calycanthaceae, is a treasure introduced from Asia before this country was a nation. Michael Dosmann, Curator of Living Collections, spoke about the plant’s history, its virtues, and the challenges it presents to northern gardeners. Find our one and only specimen at the entrance to the Explorers Garden, just off Bussey Hill Road at Accession #: 236-98*A.

TreeMob™! Hamamelis x intermedia ‘Arnold Promise’

March 2013

Arnoldia Editor Nancy Rose discussed the traditional uses of witch hazel and the origins and naming of Hamamelis x intermedia. She highlighted the cultivar ‘Arnold Promise’, Accession #: 396-69*A.

TreeMob™! Timber Bamboo and Others

March 2013

Bamboo is an evergreen woody plant with many unique features. Biao Jin, a visiting scholar from China, talked about the growth traits, ecology, and Chinese cultural uses of bamboo on Conifer Path at Accession #: 369-80*MASS, Phyllostachys bambusoides.

TreeMob™! Bornean Trees in Boston

February 2013

Cam Webb, an Arboretum researcher based in Indonesian Borneo, discussed tree genera that occur both in Southeast Asia and in New England, and what they tell us about the history of tropical rain forests and adaptation to the cold. He highlighted Accession #: 801-87*A, Diospyros virginiana, the common persimmon, south of Meadow Road and opposite Faxon Pond.

TreeMob™! A California Native Thrives in New England

January 2013

The bright green foliage of California incense cedar can enliven the dullest winter day. Calocedrus gets its name from the Greek kallos, meaning “beautiful,” and cedrus, originally from Latin meaning “evergreen conifer.” Unlike most other conifers, male cones of incense cedar shed pollen on winter’s winds. Visitor Education Assistant Maggie Redfern presented a pair of trees laden with pollen cones at the base of Peters Hill along South Street, including Accession #: 450-86*G, Calocedrus decurrens.

TreeMob™! Winter Twigs

January 2013

Most people who can identify trees have come to recognize them by their characteristic leaves, flowers, or fruit, present during the growing season. But with deciduous trees, one can’t rely on these features during the winter months. Fortunately, each species of tree has a unique signature which can be found by studying its twigs. Arborist Kyle Stephens discussed twigs and the information they hold about their identity and their growth habits, featuring Accession #: 695-80*B, Ailanthus altissima forma erythrocarpa, opposite the cork trees along Meadow Road.


TreeMob™! Sleeping Beauty: A Flower Bud Fairy Tale

December 2012

Deciduous trees appear bare, with no of leaves and flowers during the winter. However, the flowers and leaves that will appear in spring are already present, though hidden. These tiny flowers and leaves begin to grow at the end of summer and remain protected inside the bud in a state of dormancy through the winter. Then the warm kiss of spring wakes them from slumber. Visiting researcher Erica Fadon showed what is happening inside the buds of three different trees in the Bradley Rosaceous Collection, at Accession #: 931-51*A, Prunus sargentii ‘Columnaris’.

TreeMob™! Fagus sylvatica ‘Tortuosa’

December 2012

The enigmatic cultivar of the European beech, Fagus sylvatica ‘Tortuosa’, is a rarity in nature. Although now fairly common in cultivation, the tortuous habit of these trees still continues to puzzle botanists. Julien Bachelier shared the many mysteries yet to be solved at Accession #: 2420*A.

TreeMob™! Mosses: Midgets Among Giants

November 2012

Curatorial Fellow Stephanie Stuber offered the low down on mosses—some of the plant kingdom’s tiniest members. The presentation met at the summit of Hemlock Hill, near Accession #: 2328-98*A, Tsuga canadensis (Canadian Hemlock).

TreeMob™! Light in the Larches

October 2012

Sarah Mathews, Arnold Arboretum Sargent Fellow, discussed how plants sense seasonal changes and the mechanisms that triggers their responses. This mob met in the larches on Peters Hill, near the Mendum Street Gate at Accession #: 10-96*C, Larix gmelinii var. olgensis.

TreeMob™! Franklinia alatamaha

September 2012

Senior Research Scientist Peter Del Tredici discussed the Arboretum’s most spectacular accession of Franklinia alatamaha (Accession #: 2428-3*A), from its rich history to a consideration of why this species is extinct in the wild.

TreeMob™! Katsuras: Hearts of Gold

September 2012

Curator of Living Collections Michael Dosmann spotlighted the katsura collection as a prelude to autumn. Some of the Arboretum’s oldest accessioned plants (including Accession #: 882*B), katsuras display amazing fall color, and senescing leaves emit the aroma of caramel or burnt brown sugar.

TreeMob™! Blind Date

September 2012

Arboretum Director Ned Friedman and Curator of Living Collections Michael Dosmann discussed methods for determining the age of trees, and demonstrated coring techniques with a shagbark hickory on the east edge of Meadow Road.

TreeMob™! The Mighty Oaks

August 2012

Guest presenter Dave Barnett, President and CEO of Mount Auburn Cemetery, spoke about the oaks (Quercus spp.) that dominate the landscapes of both the Arnold Arboretum and Mount Auburn Cemetery. The talk took place in the Arboretum’s oak collection, north of Valley Road at the northern end of Oak Path.

TreeMob™! Ephedra minuta

August 2012

Stephanie Conway, a visiting fellow in the Friedman Lab at the Arnold Arboretum, spoke in the Leventritt Shrub and Vine Garden about this ancient species, how it is related to conifers, and where—and whether—is should rest on the gymnosperm family tree.

TreeMob™! Trouble Spot Transformed

August 2012

Manager of Horticulture Steve Schneider discussed the results of this year’s intern project at the Bussey Hill Seep. Spectators learned how and why this this overgrown and difficult to manage site has been transformed.

TreeMob™! Magnolia virginiana

August 2012

This mob met on the slope behind the Hunnewell Building to consider protogynous plant reproduction (i.e. in each flower, the female function precedes the male function) and the seeds that are produced, with visiting researcher Juan Losada.

TreeMob™! Hanging in There: How Plants Climb – Humulus lupulus ‘Cascade’

August 2012

The Leventritt Shrub and Vine Garden provided the location for plant morphologist Pam Diggle to talk about the various ways that vines attach themselves to other plants, trellises, walls, and even telephone wires.

TreeMob™! Goldenrain Tree – Koelreuteria paniculata

July 2012

Here at the Arboretum, it’s all about the backstory, and every tree has at least one. Curator of Living Collections Michael Dosmann shared a few of the special stories attached to several of our Koelreuteria paniculata (goldenrain tree) accessions.

TreeMob™! Locust, Legumes, and Nitrogen Fixation

July 2012

Arnoldia Editor Nancy Rose discussed Robinia pseudoacacia, accession 321-48*A, located near the juncture of Meadow and Bussey Hill Roads. Known commonly as black locust, R. pseudocacia hosts nitrogen-fixing bacteria in its root system, a characteristic shared by many other members of the pea family.

TreeMob™! Stewartias: Natives, Exotics, and Hybrids

July 2012

Senior Research Scientist Peter Del Tredici met visitors at the entrance to the Explorers Garden off Bussey Hill Road for a comparison between the many stewartias in the Arboretum collection. Members of the tea family of plants, stewartias are one of six species collected by the Arboretum in collaboration with the USDA and the North American Plant Collections Consortium.

TreeMob™! Plant Armor: A Thorny Issue

June 2012

This gathering at the summit of Peters Hill featured Arboretum Director Ned Friedman providing an overview of the evolutionary development of thorns in woody plants. Gleditsia triacanthos, accession 1237-79*C, served as an example of this protective adaptation.

TreeMob™! Keeping Track of Trees

June 2012

Visitors to this Tree Mob™ at the summit of Bussey Hill were introduced to the Arboretum’s plant inventory program. Kyle Port, manager of plant records, and Stephanie Stuber, curatorial fellow, explained how and why our living collections are tracked and recorded using Pinus parviflora, accession 1539-71*D, as an object lesson.

TreeMob™! Pinus densiflora

May 2012

Participants got to know Pinus densiflora, accession 1724-77*B with Research Scientist Cary Pirone. Cary explained the process of conifer reproduction and described the pollination research she is conducting at the Arboretum.

TreeMob™! Ginkgo biloba

May 2012

Senior Research Scientist Peter Del Tredici explained the reproductive biology of Ginkgo biloga at the time of day when the process is visible. Visitors met at Ginkgo biloba ‘Hayanari’, accession 824-83*A, just beyond the Hunnewell Building Visitor Center, and observed the phenomenon with hand lenses.

TreeMob™! Malus sargentii

May 2012

Arboretum Apprentice Miles Sax Schwartz introduced visitors to Malus sargentii, accession 20408*D, on Peters Hill. Miles used this plant to illustrate the Arboretum’s long interest in cultivating crabapples, including his recent efforts to reassess and reinvigorate these plants at the Arboretum.