This tree is a native of western N. America, from the borders of the Arctic Ocean to Oregon. It was introduced to Kew in 1903 by Prof. Sargent, who described it as a tree sometimes 40 ft high, with a trunk 2 ft in girth, forming a narrow head of short and nearly horizontal branches; but sometimes a mere shrub, and forming thickets; young shoots finely downy at first, and very glandular. Leaves ovate, 3 to 6 in. long, 11⁄2 to 4 in. wide, rounded or broadly wedge-shaped at the base, pointed, doubly toothed; light green above, pale, very lustrous green beneath; glabrous or with hairs along the midrib, and tufts in the vein-axils; viscid when young; stalk stout, grooved, 1⁄2 to 3⁄4 in. long. Male catkins 4 to 5 in. long. Sargent distinguishes this species among American arborescent alders by the flowers opening with or after the leaves, by the female catkins being enclosed during the winter, and by the lustrous under-surface of the leaves. It is the Western American representative of A. viridis.
From the Supplement (Vol. V)
In Farlow's mongraph this appears as A. viridis subsp. sinuata (Reg.) Löve & Löve.