Eucommia ulmoides: A Tree For Urban Areas

Trial Plantings

Thirty-four trees were planted in 6-ft treelawns along Liberty Street, in Cleveland, Ohio, in 1952 (Fig. 1). The trees had been grown from seed received from Indianapolis, Indiana, but the origin of the seed is unknown (pers. comm. John Michalko). Currently, these trees are about 14 inches dbh and from 25 to 30 ft tall. No problem has been encountered with insect pests or with limbs that droop and interfere with traffic, unlike many species of trees used in urban areas. The trees have needed little maintenance. Unusually cold temperatures of about –20°F in the city in the winters of 1977 and 1978 resulted in slight dieback in the crowns of the trees but this dieback was subsequently obscured by new growth. Winds up to 50 miles per hour at the time caused little limb breakage in the trees (pers. comm. William Killmer).

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Fig. 1.

Chinese threadtrees (Eucommia ulmoides) along Liberty Avenue, Cleveland, Ohio. Planted in 1952, the trees were photographed by William Killmer in 1974.

In fall, 1982, the city of Cleveland planted about 60 new trees that had been grown from seed collected from the Liberty Street trees. The trees were planted in narrow treelawns along a street on which salt to melt snow is applied each winter, in an industrial area where the air contains particulates originating from nearby steel mills. The possible adverse effect of these substances on survival and growth of the trees is being studied.

Trees planted at the Ohio Agricultural Research and Development Center at Wooster, Ohio, have varied in performance. Generally, they have grown quite satisfactorily, except for some small ones in the shade tree evaluation plots that were killed at temperatures of   –20°F.   These and some small trees at Indianapolis, Indiana, earlier had sustained moderate storm damage.   The species appears to be adaptable to soils ranging well above pH 7.0, but is intolerant of fine-textured soils with poor drainage (pers. comm. Davis Sydnor).

In 1972, five trees were planted by the author in a canyon campground east of Logan in northeastern Utah. Winter temperatures there regularly go to   –20°F or lower. Only two trees survived and they are no bigger now than when planted because of winter-kill of the new shoots each year.

Propagation

Propagation of Eucommia ulmoides has been no problem. Lake County Nursery Exchange, Perry, Ohio, has seed-propagated trees in general production, with quantity sale of caliper-size stock scheduled for 1985. Sexually propagated trees also are in production at Saratoga Horticultural Foundation, Saratoga, California. Softwood cuttings taken in mid-June from a mature tree in Illinois were successfully rooted (8). The benefits of root-promoting chemicals for this purpose were reviewed at a meeting of plant propagators (11).

Chemical Properties

Foote (5) described how World War I interrupted sources of supply of tu-chung bark from Eucommia ulmoides trees, the source of an unidentified “valued tonic medicine.” The article pictured a man in Yungyang Hsien, China, shouldering a wooden pole with a large bundle of this bark hanging from each end.

When a leaf of Eucommia ulmoides is broken and the pieces separated, delicate, silvery threads form between them. These threads consist of a substance that is an isomer of the hydrocarbons of rubber (7), known as gutta (2). Present in the latex of Eucommia, some Euonymous species, and several species of Malaysian trees, gutta differs from rubber in that it is plastic and not elastic. It dissolves in ether, carbon disulfide, and chloroform about twice as fast as crude rubber (10). Before dissolving, crude rubber swells greatly but retains it original proportional shape, whereas the substance from Eucommia ulmoides only softens and flattens out on the bottom of the container. Commercial Eucommia plantations, apparently for gutta production, have existed in Russia since intensive vegetative propagation of original source male plants began about 1931 (4).

Common Name

The mistaken identity of the gutta in Eucommia ulmoides and the species’ hardiness in temperate environments have resulted in the species being called, “hardy rubber tree.” For accuracy, it could be called “hardy gutta tree” or   “gutta-percha tree,” a name of long standing in Russia (12). This latter name, together with the species’ country of origin, is the basis of another common name, “Chinese Rukkis Tree” (1). The common name for this tree in China is “tu chung” (3), a name incapable of precise Engish translation. Use of the name, “Chinese treadtree,” in reference to the country of origin and to the threads that connect separated leaf parts, may increase public interest in this intriguing species. The numerous attributes of Eucommia ulmoides or Chinese threadtree contradict its relative scarcity in the United States.