RICHARDSON, K. 2020. PROMISE OF BARK: EUCOMMIA ULMOIDES. ARNOLDIA, 77(3): 40

Promise of Bark: Eucommia ulmoides

Kathryn Richardson

n July 1, 1910, Ernest Henry Wilson was however, Sargent returned to the subject with traveling through Yunyang County, a more dismal assessment, noting that the OChina—then part of eastern Sichuan plant “has been of more interest to the ener- Province—collecting plant material for the getic newspaper report than it can ever be to the Arnold Arboretum. The region is extremely manufacturer of rubber goods.” mountainous, with footpaths snaking along The Arboretum’s oldest specimen of Eucom- vertiginous river valleys, through naturally mia ulmoides (accession 14538*A) grows along formed rock tunnels, and past old fort barrack Linden Path, not far from the Hunnewell Build- sites. Wilson photographed many large trees in ing. The plant was received from James Veitch the region, and his passage was crisscrossed by & Sons nursery in 1907 and was likely collected men carrying loads of salt and other commer- on an earlier Wilson expedition. The tree now cial products. He photographed one of these graces visitors with its thick, sturdy branches men shouldering two large bundles of bark that that extend upward in a stair-like fashion. The were suspended from either end of a wooden bark is deeply ridged and furrowed, and has rod. This was a shipment of du-zhong, a medici- become a home for various moss and lichen. nal bark from the hardy rubber tree (Eucommia The elm-shaped leaves emerge in the spring. ulmoides), which was prescribed then, as it still When gently pulled apart, the leaves reveal is today, for kidney and liver ailments, among strings of latex within, each as thin as spiders’ other health issues. silk. Although Sargent’s predictions about the Wilson never observed wild populations of commercial use of this latex product would Eucommia ulmoides—the only species in its prove accurate in North America and Europe, family, Eucommiaceae—although he frequently the Flora of China indicates that the rubber-like saw two or three medium-sized trees planted product has been successfully used for insulat- near houses. Overharvesting and deforestation ing electrical cables, sealing pipes, and even were likely (and continue to be) the cause for filling teeth. Medical research has increasingly the rarity of sightings in the wild, but bark for pointed to the benefits of the bark for lowering medicine was abundant in cultivation. This blood pressure. medicinal use, however, was not the sole inter- Today, wild populations of Eucommia ulmoi- est of botanists in Europe and North Amer- des are heavily protected. The International ica. When the bark is harvested, dried, and Union for Conservation of Nature lists the spe- gently broken, a latex-like product becomes cies as vulnerable to extinction in the wild and visible. This characteristic aroused commer- estimates that fewer than one thousand mature cial interests. individuals remain in widely scattered popula- In 1911, Charles Sprague Sargent, the found- tions, mostly on steep slopes that are difficult ing director of the Arnold Arboretum, wrote, to access. Collectors on recent Arboretum expe- in the Bulletin of Poplar Information, about ditions have never witnessed the species in the considerable excitement that had arisen around wild, although, like Wilson, they have observed the species. “This is a hardy tree … to which a the trees in cultivation. Whether wild or culti- good deal of space has recently been given in vated, Eucommia provides a direct reminder the daily papers as the ‘Hardy Rubber-tree,’ and about the importance of plants beyond the gar- as a possible source of rubber in cold climates,” den walls: as medicine, as dreams of rubber, and Sargent wrote. If true, this use would provide as livelihoods for those who harvest and share a considerable breakthrough, given that com- what the plants have provided. mercial rubber was produced from a Brazilian species, Hevea brasiliensis, which could only Kathryn Richardson is a curatorial assistant at the be cultivated in the tropics. Five years later, Arnold Arboretum.