In the summer heat, mornings are blanketed by a mist that leaves the arboretum quiet and still. I softly make my way up Bussey Hill, my shoes soaked through by the morning dew that lies thick on the grass. A fawn suns itself on a patch of dirt while a family of turkeys take their morning stroll, all undeterred by my presence. It isn’t these creatures I have come to see, however, but 787-85*A, a striking mulberry tree that every morning for the past two weeks had been picked clean of fruit by squirrels.
Found all over the world, mulberries are known for their sweet fruits that resemble blackberries, and for their role as a key food source for silkworms. The tree I visited nearly every day for a month is a specimen of Morus rubra, a species native to North America. At the Arboretum it is surrounded by Morus alba trees, a species introduced from Asia. Despite their differences—glossiness of leaves, presence of hair-like structures on the underside of leaves, colors of fruit—these species are prone to hybridization, making positive identification of trees especially complex.
My goal in the summer of 2021 was to acquire a cutting of the plant, with leaves and fruit, to press for an herbarium specimen. As I approached the tree that morning as I had so many times before, the squirrels leaped off, revealing that they had picked the branches clean of ripe fruit. I could not fault them for their behavior; the idea of explaining to the council of squirrels how I needed a handful of fruits for scientific study was enough to keep my spirits up until the day I was successful in my task.
The specimens that I was finally able to collect were sent to Morris Arboretum, where researchers are engaged in long-term study of mulberry hybridity. Herbarium specimens have been crucial to research for centuries, and one of their primary uses is to identify species. While we believe our multi-stemmed Bussey Hill tree is correctly identified as Morus rubra, perhaps it is indeed a hybrid, the identity of which has taken years of growth to reveal itself.
Herbarium specimens also fill gaps in our knowledge by creating a physical timeline for plants throughout their lifespans. When I collect a specimen to later mount onto paper and file into the Arnold Arboretum’s Herbarium of Cultivated Plants, it’s with the knowledge that this specimen is intended to last hundreds of years, to be used in ways that I can’t even imagine. As for the squirrels, their interest in the mulberries is far less mysterious.
Devika Jaikumar is a curatorial assistant at the Arnold Arboretum.