A shrub up to 15 or 20 ft high, occasionally a tree twice as high, of elegant form; bark almost black, not peeling; young shoots resinous, warted. Leaves glandular, broadly ovate, rounded or slightly heart-shaped at the base, pointed, double-toothed; 1 to 2 in. long, 3⁄4 to 11⁄2 in wide; dark dull green, slightly hairy above; paler and soon almost glabrous beneath; veins in three to five pairs; stalks 1⁄4 to 1⁄2 in. long, at first somewhat hairy, then glabrous. Male catkins up to 2 in. long. Fruiting catkins 1 to 11⁄4 in. long, the lobes of the scales about equal in size, slightly downy or glabrous.
Native of western N. America; introduced in 1897 to Kew, where it thrives very well and makes a graceful small tree. It is allied to B. papyrifera, but from the smaller-growing varieties of that species it is distinguished by the bark not separating into layers, and in being almost black. The very resinous young twigs and glandular young leaves also mark it.
The B. occidentalis of Sargent is B. papyrifera var. commutata (q.v.).