As a student of horticulture in the Midwest of the US, I was fascinated by the floral characteristics of the eastern redbud (Cercis canadensis). The reddish-purple flowers and brown pea-like fruits are borne directly out of the bark of older wood of main trunks and stems rather than newly emerging growth. This phenomenon, known as cauliflory, is most prevalent in tropical species including coffee and cocoa. Although still intrigued every time I see it, I am even more enthralled by epiphylly, when flowers and fruits (as well as other structures) grow attached to leaves (often the midvein). At the Arnold Arboretum, epiphyllous flowering can be observed on a single specimen of Helwingia japonica (AA# 912*MASS) in the Explorers Garden, received in 1880, likely a propagule from the first introduction of the species into European cultivation.

Alone in the Helwingiaceae, genus Helwingia contains four species occurring from the Himalayas to Japan. Either evergreen or deciduous, all are shrubby, epiphyllous, and dioecious (bearing male and female flowers on separate plants). The Arnold’s 1880 specimen is male, and currently lacks a paired female plant for successful reproduction.

In 2018, I traveled to the Shennongjia region of Hubei Province, China, as part of the North America-China Plant Exploration Consortium. Along with important germplasm for conservation, we collected seeds of two species of Helwingia: H. japonica and H. chinensis. Both were found growing on shaded rock outcrops in rich pockets of humus soil in association with the conifer Torreya fargesii.

Helwingia japonica’s broad, deciduous leaves sport umbels of tiny, four-petaled flowers in spring, developing into pea-sized black drupes in autumn. Helwingia chinensis, by contrast, is a semi-evergreen species with narrow leaves bearing purplish male flowers on long stalks (pedicels) in groups of 4-5; female flowers are nearly sessile (unstalked) and in groups of 1-3 with fruits ripening to a glossy cherry red.

We now have one plant from each species in the Arboretum’s Dana Greenhouses. The H. chinensis plant, a male, bloomed copiously this year. Over the past 150 years, we have made several attempts to cultivate this species in the collections—each to no avail. If this collection is successful, we’ll need to find it a mate by collecting it again.

Andrew Gapinski was Director of Horticulture at the Arnold Arboretum from 2013 to 2023.

From “free” to “friend”…

Established in 1911 as the Bulletin of Popular Information, Arnoldia has long been a definitive forum for conversations about temperate woody plants and their landscapes. In 2022, we rolled out a new vision for the magazine as a vigorous forum for tales of plant exploration, behind-the-scenes glimpses of botanical research, and deep dives into the history of gardens, landscapes, and science. The new Arnoldia includes poetry, visual art, and literary essays, following the human imagination wherever it entangles with trees.

It takes resources to gather and nurture these new voices, and we depend on the support of our member-subscribers to make it possible. But membership means more: by becoming a member of the Arnold Arboretum, you help to keep our collection vibrant and our research and educational mission active. Through the pages of Arnoldia, you can take part in the life of this free-to-all landscape whether you live next door or an ocean away.

For more tree-entangled art, science, and writing, subscribe to Arnoldia by becoming a member of the Arnold Arboretum.