Betula chinensis Maxim.

Betula chinensis is known from northeastern China, where it is found from near Beijing to possibly as far west as Gansu, and from Korea. The species was named in 1879 from specimens collected near Beijing by Emil Bretschneider (1833–1901), the Russian physician and botanist best known for his account of European botanical encounters with the Chinese flora (Bretschneider 1898). Flora of China describes the species’ habitat as ‘broad-leaved forests in mountain valleys [and] shaded, rocky mountain slopes’, noting also that it constitutes one of the most valuable timber trees in north China, the wood being ‘hard and dense, close-grained, very fine textured, used for making pestles and wagon axles’ (Li & Skvortsov 1999). In Korea it appears to be a shrub of exposed mountain ridges (McAllister & Ashburner 2013).

With its relatively small, more-or-less rhomboid or diamond-shaped, coarsely toothed leaves, Betula chinensis most resembles B. dahurica or B. gmelinii, but is distinguished by its distinctive fruiting catkins, which are more or less spherical when mature, reminiscent of those of B. costata, and very similar to, but somewhat smaller than, those of B. globispica or B. fargesii. The fruiting catkin scales have elongated lobes, and are more or less glabrous except for marginal cilia and the base of the abaxial surface, but lack the apical twisted hair tuft characteristic of the B. potaninii species group. Betula chinensis is easily distinguished from its close relatives by the thin texture of the leaves and flexibility of the shoots, and by the twigs, which are thinner than the broad buds. Also diagnostic is the unmistakable crowding of the lenticels on trunks and branches, rivaled only by B. schmidtii (but that is usually a substantial tree). Another unusual feature of this species, shared with its close relation Betula globispica, is that only one seed is produced in the axil of each fruiting catkin scale (de Jong 1992). The species appears to occurs in both octoploid and hexaploid cytotypes (McAllister & Ashburner 2013).

In cultivation Betula chinensis makes a shrub or small tree of very variable habit. Some individuals form low, spreading shrubs of no more than about 2 m while others are more upright. A plant raised from W 10707 at RBG Edinburgh grew to around 6 m (Bean 1976). The breaking buds in spring and young shoots are sensitive to frost, and the thin twigs and buds are susceptible to winter desiccation. In many parts of Britain young shrubs are often reduced to a tangle of dead twigs, but the species might thrive better in the more continental climates of mainland Europe or North America. Bean (1976) reported its first introduction from the Arnold Arboretum in 1920. There is a fine specimen in the Sir Harold Hillier Arboretum and other more recent introductions from Korea are now growing well in a number of gardens. At Ness Botanic Garden, young plants from Chiak-San put out on a dry sunny slope in sandy soil have thrived and develop attractive orange-yellow autumn colour. They bore their first fruiting catkins in their sixth year. Older, established plants show less dieback in winter and bud break seems to be sufficiently delayed to avoid damage by late spring frosts. On these plants only the male catkins appear to be seriously damaged by desiccating winter wind. Young plants are fairly shade-tolerant but mature trees are less so and shaded branches die, the dead wood remaining fairly tough, unlike that of most other birches.

Like its relatives, Betula chinensis has a very vigorous, deep root system, perhaps more so than any other birch. The species’ natural habitat suggests that established bushes on deep soils ought to be tolerant of both drought and (given adequate summer warmth and a long growing season) exposure. In the nursery it is best to transplant them every year to promote the development of a compact root system. Propagation by cuttings is relatively easy, but plants appear to be almost totally self incompatible, in cultivation requiring two clones to produce viable seed.