Distribution. Coast of Alaska from Cook Inlet southward to the head of the Lynn Canal.
7. [Betula alaskana] Sarg. White Birch.
Leaves rhombic to deltoid-ovate, long-pointed, truncate, rounded or broadly cuneate, or on leading shoots occasionally cordate at the entire base, coarsely and often doubly glandular-serrate, thin, dark green above, pale and yellow-green below, 1½′—3′ long, 1′—1½′ wide, with a slender midrib and primary veins pubescent or ultimately glabrous below; petioles often bright red, somewhat hairy at first, finally glabrous, about 1′ long; Flowers: staminate aments clustered, sessile, 1′ long, ⅛′ thick, with ovate acuminate scales puberulous on the outer surface, and bright red, with yellow margins; pistillate aments slender, cylindric, glandular, 1′ long, ⅛′ thick, on stout peduncles nearly ½′ in length. Fruit: strobiles glabrous, pendulous or spreading, 1′—1¼′ long, ⅓′—½′ thick, their scales ciliate on the margins; nut oval, narrower than its broad wing.
A tree, usually 30°—40°, occasionally 80°, high, with a trunk 6′—12′ in diameter, slender erect and spreading or pendulous branches, and glabrous bright red-brown branchlets more or less thickly covered during their first year with resinous glands sometimes persistent until the second or third season. Winter-buds ovoid, obtuse at the gradually narrowed apex, about ¼′ long, with light red-brown shining outer scales sometimes ciliate on the margins, and oblong rounded scarious inner scales hardly more than ½′ long when fully grown. Bark thin, marked by numerous elongated dark slightly raised lenticels, dull reddish brown or sometimes nearly white on the outer surface, light red on the inner surface, close and firm, finally separable into thin plate-like scales.
Distribution. Valley of the Saskatchewan northwestward to the valley of the Yukon, growing sparingly near the banks of streams in forests of coniferous trees and in large numbers on sunny slopes and hillsides; the common Birch-tree of the Yukon basin.
× Betula commixta Sarg., a shrub, growing on the tundra near Dawson, Yukon Territory, is believed to be a hybrid between B. alaskana and B. glandulosa Michx.
8. [Betula fontinalis] Sarg. Black Birch.
Leaves ovate, acute or acuminate, sharply and often doubly serrate, except at the rounded or abruptly cuneate often unequal base, and sometimes slightly laciniately lobed, pale green, pilose above, and covered by conspicuous resinous glands when they unfold, at maturity thin and firm, dark dull green above, pale yellow-green, rather lustrous and covered by minute glandular dots below, 1′—2′ long, ¾′—1′ wide, with a slender pale midrib, remote glandular veins, and rather conspicuous reticulate veinlets; turning dull yellow in the autumn; petioles stout, puberulous, light yellow, glandular-dotted, flattened on the upper side, often flushed with red, ⅓′—½′ long; stipules broadly ovate, acute or rounded at apex, slightly ciliate, bright green, soon becoming pale and scarious. Flowers: staminate aments clustered, ½′—¾′ long and 1/16′ thick during the winter, with ovate acute light chestnut-brown scales pale and slightly ciliate on the margins, becoming 2′—2½′ long, and about ⅛′ thick, with apiculate scales; pistillate aments short-stalked, about ¾′ long, with ovate acute green scales; styles bright red. Fruit: strobiles cylindric, rather obtuse, puberulous or nearly glabrous, 1′—1¼′ long, ½′ thick, erect or pendulous on slender glandular peduncles, ¼′ to nearly ¾′ in length; their scales ciliate, puberulous, the lateral lobes ascending, shorter than the middle lobe; nut ovoid or obovoid, puberulous at apex, nearly as wide as its wing.