圆叶桦 yuan ye hua

Betula glandulosa Michaux var. rotundifolia (Spach) Regel.

Shrubs to 2 m tall; bark gray-black. Branches dark gray, glabrous, densely yellow resinous glandular; branchlets red-brown, densely white pubescent and resinous glandular. Petiole 5-7 mm, slender, densely pubescent; leaf blade suborbicular, rarely broadly obovate, 1-2.5 × 0.8-2 cm, both surfaces glabrous and densely resinous punctate, base rounded or broadly cuneate, margin obtusely serrate, apex subrounded; lateral veins 3 or 4 on each side of midvein. Female inflorescence erect, oblong-cylindric, 1.5-2.4 cm × 6-8 mm; peduncle 3-4 mm, densely pubescent; bracts circa 6 mm, ciliate, 3-lobed, middle lobe oblong, lateral lobes slightly spreading, elliptic, slightly shorter than middle lobe. Nutlet oblong, circa 2.5 × 1.8 mm, with membranous wings slightly narrower than nutlet. Fl. Jun-Jul, fr. Jul-Aug. 2n = 28

Thickets on mountain slopes; ca. 2300 m. Xinjiang (Altay Shan) [Kazakhstan, N Mongolia, Russia (Siberia)].

A. K. Skvortsov believes that this species should be treated as a variety of the circumboreal Betula nana Linnaeus.