J. Arnold Arbor. 3: 206. 1922.
Trees, to 25 m, crowns narrow. Bark of young trunks and branches reddish-brown, when mature becoming pinkish white to light red (starkly white in interior Alaska; D. F. Murray, pers. comm.), smooth, exfoliating in thin sheets. Twigs glabrous, covered with conspicuous resinous glands. Leaf-blade deltate-ovate with 5–18 pairs of lateral-veins, 3–8 × 2–6 cm, base rounded or broadly cuneate, margins coarsely doubly serrate, apex long-acuminate; surfaces abaxially glabrous to sparsely pubescent, pubescent along major veins and in vein-axils, covered with small resinous glands. Infructescences pendulous, cylindric, 2–4 × 0.8–1.2 cm, shattering with fruits in fall; scales glabrous, margins ciliate, lobes diverging distal to middle, central lobe narrower and equal to or slightly shorter than lateral lobes, lateral lobes broadly angular, extended. Samaras with wings broader than body, broadest near summit, extended beyond body apically. 2n = 28.
Phenology: Flowering late spring.
Habitat: Rocky or peaty slopes, bog margins, sandhills, open woods
Elevation: 100–1200 m
Alta., B.C., Man., N.W.T., Ont., Sask., Yukon, Alaska.
Betula neoalaskana belongs to a circumpolar complex including B. pendula Roth and B. populifolia Marshall (but not B. papyrifera Marshall, with which it has sometimes erroneously been merged). It is most closely related to the Asian members of this group, including B. japonica Siebold, B. mandshurica (Regel) Nakai, and B. platyphylla Sukaczev (T. C. Brayshaw 1976). The species was formerly widely known by the name B. resinifera (Regel) Britton, but that name has been shown to be illegitimate (B. Boivin 1967–1979, 15: 414–418; J. R. Dugle 1969). The name was based on a mixture of Siberian and North American material and has never been lectotypified.
Betula neoalaskana Sargent is known to hybridize with B. papyrifera Marshall, producing B. ×winteri Dugle, and with B. glandulosa, producing B. ×uliginosa Dugle.
"broadest" is not a number. "broader" is not a number.