Betula calcicola (W.W.Sm.) P.C.Li

Betula calcicola is fairly easily distinguished by the extreme hairiness of its young shoots and almost circular leaves, both of which are densely covered in white to golden brown hairs. The leaves are deep green, rather leathery in texture, with deeply impressed veins; many persist on the twigs throughout the winter, decaying slowly so that entire leaves are always present beneath the plants. The fruiting catkins also persist over the winter and the nutlets have only a rudimentary wing. The species is found primarily on the Lijiang Range in northwest Yunnan on limestone rocks and cliffs at high altitude, often in mossy crevices with Pleione sp., Primula forrestii and various small shrubs (in Flora of China it is also recorded from southwest Sichuan). It was originally described as a variety of Betula delavayi from a 1910 George Forrest collection, it was raised to species rank by P. C. Li in 1979.

Betula calcicola can only really be confused with Betula bomiensis, in which the young shoots are much less densely hairy and the leaves smaller. Betula delavayi also has much less densely hairy shoots and leaves, larger fruiting catkins and seeds, and usually larger, more elongated, flatter leaves. Betula potaninii has much smaller, narrower leaves with more numerous veins, less hair, and much smaller fruiting catkins. Betula potaninii and B. calcicola are the only species with male catkin scales attached at their bases (not centrally) and thin triangular tips to the scales of the fruiting catkins; in other birch species (perhaps with the exception of B. ashburneri and species of section Acuminatae) the tip is thicker and the same texture as the rest of the scale.

The species was not introduced into cultivation until 1981 by Roy Lancaster, though a series of further collections followed from the same region. The Chungtien, Lijiang & Dali expedition collected it in 1990 (CLD 791, grown at RBG Edinburgh and the Sir Harold Hillier Gardens), as did the Sino-British Lijiang Expedition in 1987 (SBL 272) and AGS Expedition to China in 1994 (ACE 2387). Also grown at Hillier’s is a Brickell and Leslie collection from 1987 (B&L 12268).

In cultivation, seed-raised plants have grown to 4 m in ten years, but vary widely in habit, some being fastigiate with strong leading shoots, producing attractive, narrow, upright small trees in cultivation, while others are more spreading, with the leading long shoots arching outwards as in the related B. potaninii, B. bomiensis and B. chichibuensis. The plants do not tolerate drought or waterlogging, requiring full sun and light, well-aerated but moist, preferably humus-rich soil. Although the buds do not break particularly early in spring, the young shoots are tender and are often damaged by late frosts. Many of the male catkins fail to expand in spring, either the terminal part or the whole catkin, apparently owing to desiccation during the winter, which affects pollen production and seed set.