22. Betula pendula Roth, Tent. Fl. Germ. 1: 405. 1788.
垂枝桦 chui zhi hua
Betula verrucosa Ehrhart.
Trees to 25 m tall; bark grayish white, exfoliating in sheets. Branches usually pendulous, dark brown, slender, glabrous, shiny; branchlets brown, slender, glabrous, sparsely resinous glandular or not. Petiole slender, 2-3 cm; leaf blade triangular-ovate or rhombic-ovate, 3-7.5 × 1.5-6 cm, abaxially densely resinous punctate, adaxially glabrous, base truncate, broadly cuneate, or cuneate, margin coarsely or incised doubly serrate, apex acuminate or caudate-acuminate; lateral veins 6-8 on each side of midvein. Female inflorescence oblong or oblong-cylindric, 1-3.3 cm × 8-10 mm; peduncle pendulous, 1-2 cm; bracts 5-6 mm, densely pubescent, ciliate, 3-lobed, middle lobe ovate or triangular-ovate, lateral lobes recurved, slightly longer than middle lobe. Nutlet obovate-elliptic, ca. 2 × 1 mm, sparsely pubescent, with membranous wings slightly longer than and ca. 2 × as wide as nutlet. Fl. Jun-Jul, fr. Jul-Aug. 2n = 28, (42), 56.
Temperate broad-leaved forests; 500-2300 m. N Xinjiang (Altay Shan) [Kazakhstan, Mongolia, Russia (W Siberia); Europe]
May easily be confused with Betula platyphylla; however, in that species, the branches are not pendulous and the wings of the nutlet are about as wide as the nutlet. The name B. alba Linnaeus, nom. rej. prop., has been widely and persistently misapplied in the sense of B. pendula; the lectotype of B. alba belongs to the species currently known as B. pubescens Ehrhart, which does not occur in China.