Eucommia ulmoides Oliv.

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Credits

Julian Sutton (2023)

Recommended citation
Sutton, J. (2023), 'Eucommia ulmoides' from the website Trees and Shrubs Online (treesandshrubsonline.org/articles/eucommia/eucommia-ulmoides/). Accessed 2024-06-17.

Common Names

  • Gutta-percha Tree
  • Hardy Rubber Tree
  • Chinese Thread Tree
  • Stone Cotton Tree

Infraspecifics

Other taxa in genus

    Glossary

    IUCN
    World Conservation Union (formerly the International Union for the Conservation of Nature).
    latex
    Colourless or milky sap produced by some plants (e.g. many Apocynaceae Euphorbiaceae Moraceae).
    androdioecious
    With only male or only hermaphrodite flowers on individual plants.
    key
    (of fruit) Vernacular English term for winged samaras (as in e.g. Acer Fraxinus Ulmus)
    latex
    Colourless or milky sap produced by some plants (e.g. many Apocynaceae Euphorbiaceae Moraceae).
    lustrous
    Smooth and shiny.

    References

    Credits

    Julian Sutton (2023)

    Recommended citation
    Sutton, J. (2023), 'Eucommia ulmoides' from the website Trees and Shrubs Online (treesandshrubsonline.org/articles/eucommia/eucommia-ulmoides/). Accessed 2024-06-17.

    Deciduous medium-sized tree to 20 m. Bark grey-brown, coarsely fissured. Branches spreading, crown more or less dome-shaped. Branchlets hollow; young branchlets yellow-brown, pubescent at first, becoming glabrous; older branchlets with conspicuous lenticels. Buds shiny red-brown; scales 6–8, margin puberulous. Leaves alternate, hanging, without stipules, containing latex. Leaf blade (5–)7–15(–18) × 2.5–7(–10) cm, pinnately veined with 6–9 pairs of lateral veins, usually elliptic, sometimes tending towards ovate, obovate, oblong or lanceolate; base rounded to cuneate; margins serrate with gland-tipped teeth, apex acuminate; brown-pubescent at first, glabrous and glossy later; petiole 1–2.5 cm, sparsely villous. Plant dioecious; flowers solitary and stalked in the axils of bracts, below the upper leafy portions of the shoots, greenish brown, lacking petals and sepals. Male flowers crowded, with (5–)6–12 linear, glabrous stamens; filaments ~1 cm long, greenish yellow; anthers grey-black. Female flowers solitary or less crowded, bright green, ovary ~1 cm long, glabrous, 1-celled with 2 ovules, style terminal, 2-lobed, white. Fruit a samara, 2.5–3.5 × 1–1.3 cm, ellipsoid, with narrow, longitudinal wings. Seed 1.3–1.5cm × 0.3 cm. Flowering March–May (China), April–May (UK); fruiting Jun–November (China). (Zhang, Zhang & Turland 2003; Andrews 2009).

    Distribution  China Gansu, Guizhou, Henan, Hubei, Hunan, Shaanxi, Sichuan, Yunnan, Zhejiang

    Habitat Forests, thickets, lower mountain ridges and valleys, dry ravines, fields, 100–2000 m asl; also widely cultivated and locally becoming naturalized.

    USDA Hardiness Zone 4b-7

    RHS Hardiness Rating H7

    Conservation status Vulnerable (VU)

    Eucommia ulmoides is the hardiest, indeed the only temperate-zone tree ever used in commercial rubber production. It also has great significance in China as a medicinal plant. These economic uses, along with its isolated taxonomic position, are enough to make it an interesting tree for larger collections. However, its broad, spreading crown, lustrous pointed leaves, its cold-hardiness and tolerance of a wide range of soil conditions, together make this an attractive shade tree or ornamental specimen for more general planting.

    The species was first described scientifically by Oliver (1890) from non-flowering and fruiting specimens collected in Hubei by Augustine Henry. Flowering specimens collected in NE Sichuan by the missionary Paul Farges later allowed a refined description (Oliver 1895). The specific epithet derives from a sense that ‘the fruit and general aspect of the specimens at once suggest Ulmaceae’ (Oliver 1890). This odd plant’s relationships remained uncertain for many years (see genus introduction).

    E. ulmoides has been well known in China for far longer, due to its medicinal uses (see below). Destruction of wild plants by over-enthusiastic bark collecting, coupled with a long history of small and larger scale planting blurring the line between the wild and the cultivated, have made its wild status quite difficult to gauge (IUCN 2023). While some in the West repeat a claim that it is now unknown in the wild (e.g. Dirr 2009; Edwards & Marshall 2019), a 2018 IUCN assessment concluded that fewer than 1,000 mature, wild trees remain, in small, scattered populations (IUCN 2023).

    Bark in particular, but also leaves, seeds and male flowers, have been used medicinally in China for at least 2,000 years. The bark preparation is called du zhong. Major applications have been in nourishing the liver and kidneys, and strengthening tendons and bones, although a bewildering range of other traditional uses of the plant are documented. Huang et al. (2021) list treatment of lumbar pain, knee pain, osteoporosis, paralysis, intestinal haemorrhoids, vaginal bleeding, itching in the vagina or scrotum, dampness and residual draining of urine, spermatorrhoea, soreness and pain in the feet, and fungal infections of the foot, as well as for inducing abortion, improvement of learning and memory abilities, and anti-aging. Given this plethora of uses, it is no surprise that bark collection in particular continues to be a significant industry. The stringy inner bark is used. Bark strips are harvested in April when they are most easily peeled off the tree. They are bundled up, placed under straw for a week to sweat, then sun-dried until the inner bark can be peeled off the outer (Forrest 1995). Farmers are careful to avoid ring-barking plantation-grown trees, but opportunistic collectors might not be so careful. Forrest (1995) shows a photograph of Eucommia trees at Hangzhou Botanical Garden, their trunks swaddled against bark theft. A great deal of work has gone into exploring possible therapeutic effects of an extraordinarily diverse range of substances found in this plant (Wang et al. 2019). ‘Diverse’ is the key word here, such is the broad focus of its traditional uses.

    Eucommia ulmoides is a rubber-producing plant, although not the source of gutta-percha as its common name might imply. The polymer trans-1,4-polyisoprene is found throughout the plant as silvery, elastic threads in lactifers (Liu et al. 2022). When a leaf is broken across, one half can be made to hang in the air from the other by these almost invisible threads, which can coalresce into a thicker strand of rubber (Bowles 1914; Andrews 2009). Latex does not flow from wounded tissue, so it cannot be harvested by tapping. The rubber has to be extracted: early methods were mechanical, solvent extraction is the norm today, and use of microbes to digest the surrounding tissues is being investigated (Liu et al. 2022). Eucommia rubber has some chemical similarities to conventional Hevea rubber; physically it is both elastic and a thermoplastic. It has had some limited use in China: Zhang, Zhang & Turland (2003) note lining oil pipelines, electrical insulation and – intriguingly – filling teeth) but at times of high rubber demand there has been much wider interest in its possibilities across the temperate world.

    The first such period was in the late 19th and early 20th centuries, driven in part by demand for rubber tyres, and led to the Amazon Hevea-rubber boom which ended abruptly around 1912 when plantations in British-ruled Malaysia established from smuggled Hevea seeds came on stream. Enthusiasts in industrialised temperate-zone countries, such as John Parkin in Britain, explored the possibility of using Eucommia for home-produced rubber, but while the tree proved growable, extraction proved uneconomic (Andrews 2009). In the 1920s and 30s, the Soviet Union (which had no tropical territory or colonies) attempted large scale cultivation in Kazakhstan, Turkmenistan, Transcaucasia and Ukraine; synthetic rubbers may have been the downfall of this project (Andrews 2009). Today, with demand for rubber high, Chinese research focuses on both novel extraction methods and new uses for chemically modified Eucommia rubber, including shape-memory materials, composite films, and tyres (Liu et al. 2022).

    This is a dioecious species with insignificant flowers. There seems never to have been any doubt over its being wind-pollinated. The flowers appear with the new leaves, before they are fully expanded, and are near the base of each emerging shoot, so the clusters of expanding leaves are ringed by greenish flowers. Sex is apparently genetically determined, with roughly equal numbers of male and female trees (Wang et al. 1999), despite an early dearth of females in Western cultivation (Bean 1981). Females have a higher latex content in the leaves, so development of molecular markers to identify them early when setting up plantations is desirable (Wang et al. 2020). The winged fruit, reminiscent of an elm (Ulmus) is presumably dispersed by wind.

    As a cultivated ornamental the Gutta-percha Tree is more than merely interesting. Perhaps its most amusing usage was recorded by the great plantsman E.A. Bowles, who grew it by the gate of his garden at Myddelton House near Enfield, Middlesex, where it was ‘useful to speed a departing guest… You say, “But have you seen the hardy Rubber plant? No? Then come along,” and you move briskly to the place and pluck a leaf and roll it, and then pull it asunder and the latex forms gummy strings that harden in the air… When interest flags a little you ask “Woudn’t you like a few leaves to take home with you?” and the departure of the most lingering visitor generally follows soon afterwards.” (Bowles 1914). More prosaically, Dirr & Warren (2019) summarize its virtues and limitations nicely, ‘a handsome green shade tree’ whose ‘lack of any specific ornamental display works against it’. Even in parts of North America known for fall colour, it puts on no autumn display, at best becoming yellowish (Dirr 2009). Superbly cold-hardy, it is tolerant of drought, intense summer heat, and a wide range of soil pH; it grows in full sun or light shade but waterlogged soils are not recommended (Missouri Botanical Garden 2020; Dirr 2009). Pests and diseases are rarely a problem, although Dirr (2009) notes unexplained branch dieback in some specimens.

    E .ulmoides was introduced to Europe in the mid-1890s as seed sent by Paul Farges, probably directly to Maurice de Vilmorin at what is now the French Arboretum National des Barres. Vilmorin gave a plant to Kew in 1897 (it no longer exists, but plants probably raised from cuttings do); the Vilmorin nursery first offered material in 1902–3, by which time its great hardiness was known (Andrews 2009). Further introductions, from cultivation in W Hubei, were made by Ernest Wilson (Wilson for Veitch 629 of 1900, and W 383 of 1907 for the Arnold Arboretum (Sargent 1913; Andrews 2009). It was a feature in E.A. Bowles’s garden by 1909 (Allan 1973), though its origin is unknown. Wilson’s collections established the species firmly in Western collections, although it is less clear where some later rubber-boosters obtained seed for their experiments. For example, Willoughby Smith had an established plantation of 600 trees on his East Devon estate by 1934 (fide Andrews 2009). Large, early specimens are scattered across the British Isles with a southerly and easterly bias, perhaps the result of faster growth in warmer summers. Specimens include ones at Cambridge University Botanic Garden (17 m × 193 cm, 2014), Hergest Croft, Herefordshire (planted 1930, 13 m × 223 cm in 2013) and a multistemmed tree at Maidwell Hall, Northamptonshire (17 m × 293 cm, 2014 – The Tree Register 2023). Specimens are found across mainland Europe, including in Mediterranean gardens and in cold, continental areas; an attractive if somewhat leaning example at the University of Potsdam Botanical Garden, Germany, was measured at 10 m × 101 cm in 2020 (monumentaltrees.com 2023).

    The first introduction to North America was to the Arnold Arboretum, a plant sent from the Veitch nursery, presumably derived from Wilson’s No. 629. It still exists (accession 14538*A), a handsome if rather one-sided male tree, illustrated here (Richardson 2020; Andrews 2009). Wilson’s W 383 followed, but this remained a rare species until the 1980s (Jacobson 1996), since when it has achieved a modest distribution through nurseries and is sometimes seen as a shade tree in public places. Hardy across much of the United States and southern Canada, it grows more slowly in the Southeast than in areas with colder winters (Dirr 2009).

    Seed requires 2–3 months cold stratification for germination (Dirr 2009). Cuttings are definitely feasible; Bean (1981) recommends semi-ripe wood with gentle heat.


    'Empozam'

    Synonyms / alternative names
    Eucommia ulmoides EMERALD POINTE™

    A narrowly upright, more compact-crowned selection, smaller than usual at maturity, to perhaps 12 m height and 4.5 m spread; marketed as a very hardy, adaptable street tree. Leaves smaller than typical, more deeply serrate, with a wavy margin and thicker texture. The leaf surface is more deeply textured, almost rugose. Introduced 2009 by Lake County Nursery, OH. (Dirr & Warren 2019; Dirr 2009; Lake County Nursery 2023)