17.
Betula nana
Linnaeus, Sp. Pl. 2: 983. 1753.
Arctic dwarf birch, bouleau nain
Shrubs , sprawling, creeping, or upright, to 1 m. Bark gray to dark brown, smooth, close; lenticels inconspicuous, unexpanded. Twigs without taste and odor of wintergreen, glabrous to sparsely or moderately pubescent, with or without heavy resinous coating, sometimes covered with warty resinous glands. Leaf blade broadly orbiculate or obovate-orbiculate to reniform, with 2--6 pairs of lateral veins, often broader than long, base rounded to nearly cordate, margins deeply crenate, apex rounded; surfaces abaxially glabrous to sparsely or moderately pubescent. Staminate and pistillate catkins produced season before flowering but retained in buds during winter, expanding along with new growth in spring. Infructescences erect, nearly cylindric, shattering with fruits in fall. Samaras with wings much narrower than body, broadest near center, not extended beyond body apically.
Subspecies 3 (2 in the flora): subarctic and arctic of North America, Europe, and Asia.
