Betula ermanii Cham.

Betula ermanii, Rock Birch, is one of the finest and most distinct of birches, essentially a mountain tree in its natural state, and a major, if not the sole component of tree-line forest in Japan and Korea and mainland eastern Asia as far west as Lake Baikal. Those fortunate enough to have seen the species growing in the wild in Japan, and perhaps climbed through the open forest which clothes the slopes of the mountains of Hokkaido, will have found the ‘limby’ shapes of the spreading trees flattened by snow, and reduced to elfin proportions at their altitudinal limit. The autumn colour is a superb yellow, highlighted against dark Pinus pumila, and contrasted with the vivid reds and oranges of suckering Sorbus matsumurana. The freshness of the young spring foliage surpasses even that of cultivated plants.

This species was first described by Chamisso in 1831, from specimens collected in Siberia by the physicist Georg Adolf Erman (1806–1877), an intrepid traveller who decided in 1828 to travel around the world, departing with the expedition led by Christopher Hantseen, which was to carry out magnetic measurements in Siberia. When the Hantseen expedition turned back at Kyakhta on the Mongolian border, south of Lake Baikal, Erman proceeded onward at his own expense to Yakutsk and Okhotsk, crossing the Sea of Okhotsk to Kamchatka and then over the peninsula to the port of Petropavlovsk, where he met the ship of Leontii Hagemeister, who was supplying Russian colonies in Alaska. Erman travelled with Hagemeister to Sitka (where he saw sea otters) and then on to San Francisco, Tahiti, the coast of South America, and finally around the Horn to Europe. On his return to Germany, he wrote up his discoveries, which were published in a five-volume account (Erman 1833, 1835, 1838, 1841, 1848​​).

Betula ermanii has been cultivated in Britain since it was introduced shortly before 1900, probably from mainland northeast Asia, though trees of continental provenance have always been found susceptible to frost damage due to early bud break (Bean 1976). However, a recent collection from the Russian Far East, Prymorsky Kraj, Olchovaja Mountain has reached about four metres at Ness Botanic Garden. In Britain, trees of (presumably) Japanese and Korean origin form beautiful large specimens with creamy- to pinkish-white bark peeling off in large sheets; material with this provenance tends to have a quite distinctive appearance, due to the relatively warty twigs with few long silky hairs and resinous buds. Collections from further north in China and the Russian Far East are often referred to var. lanata and have conspicuous large, grey-hairy buds, more hairy, less resinous twigs, and less sharply toothed leaves. Experience at Ness suggests that the species may be less tolerant of drought than many others, at least when grown on its own roots. The vernacular name Rock Birch – from the Russian name – is derived from the species’ ability to colonise poor, skeletal soils, though in such situations they tend to remain shrubby (Bean 1976), the conservative habit enabling them better to cope with environmental stress. A number of cultivars are available, discussed in detail below. The cultivar-like name ‘Saitoana’ is sometimes used (incorrectly) to refer to plants raised from a collection by Mark Fillan (MSF 865) (Bartlett 2019).

Var. subcordata (Regel) Koidz. – found sporadically throughout Japan, and collected from Sakhalin by E. H. Wilson (W 7338) – is treated by POWO (POWO 3/6/2026) as a synonym of B. grossa. Var. japonica, said by Bean to have 14–15 vein pairs, is treated by McAllister and Ashburner (2013) as a synonym of B. ermanii var. ermanii.