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A tree said to become 100 ft high; bark of the trunk peeling, creamy or pinkish white; that of the branches orange-brown; young shoots not downy, but with numerous glandular warts; buds nearly 1⁄2 in. long, viscid, slender-pointed. Leaves broadly ovate, with a straight or slightly heart-shaped base, taper-pointed, coarsely triangular-toothed; 2 to 3 in. long, 11⁄2 to 21⁄4 in. broad; freely specked with glands on both surfaces, and nearly glabrous except for hairs on the midrib, veins, and vein-axils beneath; veins in seven to eleven pairs; stalk 1⁄2 to 1 in. long, warted. Fruiting catkins barrel-shaped, 1 to 11⁄4 in. long, 1⁄2 to 5⁄8 in. wide, the three lobes of the scales broadest at the rounded ends.
A native of E. Asia from the Kamchatka peninsula through Pacific Russia to Korea, Japan, and Manchuria, and westward in Siberia as far as Lake Baikal. In favourable habitats it grows to 75 ft or more high, but becomes shrubby at high altitudes and near the northern end of its range, and is capable of colonising thin and poor soils – hence the Russian name for it, which means ‘rock birch’. The bark varies in colour from white to grey or pale pinkish brown, and peels in thin sheets. According to Wilson, who studied this birch during his visit to Japan in 1914, it usually divides into several stems near the base, but develops a clean trunk and narrow crown when crowded.
This birch is extremely variable in shape, size, and toothing of leaf. The var. subcordata (Reg.) Koidz., as interpreted by Schneider, is really a miscellany of Japanese and mainland forms which have little in common except that they differ in one respect or another from the type. However, one variety (included by Schneider in var. subcordata) appears to be distinct. This is:
specimens: Kew, Pinetum, 56 × 43⁄4 ft (1982); Windsor Great Park, 77 × 41⁄2 ft (1979); Grayswood Hill, Haslemere, Surrey, 63 × 111⁄2 ft at base (1966); Westonbirt, Glos., 70 × 91⁄4 ft (1979); Hergest Croft, Heref., 62 × 31⁄4 ft (1978); Bodnant, Gwyn., 55 × 53⁄4 ft (1981); Brook House, Co. Londonderry, 50 × 51⁄2 ft (1976).
A race of B. ermanii, said to be confined to the Korean island of Cheju Do (Quelpaert), was given specific rank by Nakai as B. saitoana. However, this was reduced by Schneider to the rank of a subvariety of the typical variety of B. ermanii (B. e. var. genuina Reg. subvar. saitoana (Nakai) Schneid.). It differs in its much smaller leaves, up to 2 in. long, with only six to eight pairs of lateral veins.
Another, more distinct, variant of B. ermanii is var. lanata Reg., in which Schneider included B. e. var. tomentosa Reg., described by Regel at the same time. In this the twigs are downy or finely woolly when young; the leaves triangular-ovate, with mostly seven to nine pairs of veins, on downy petioles; the bracts of the fruiting catkins are markedly ciliate, and are downy on the outer side. Native of eastern Siberia and the Russian Far East. It has been given specific rank as B. lanata (Reg.) Vassiliev.
B. bhojpattra var. japonica Shirai
B. nikoense Koidz