white alder

Alnus rhombifolia is a medium-sized deciduous tree growing to 15–25 metres (49–82 ft) (rarely to 35 metres (115 ft)) tall, with pale gray bark, smooth on young trees, becoming scaly on old trees. The leaves are alternate, rhombic to narrow elliptic, 4–10 centimetres (1.6–3.9 in) long and 2–5 centimetres (0.79–1.97 in) broad, with a finely serrated margin and a rounded to acute apex; they are thinly hairy below. The flowers are produced in catkins. The male catkins are pendulous, slender, 3–10 centimetres (1.2–3.9 in) long, yellowish, and produced in clusters of two to seven; pollination is in early spring, before the leaves emerge. The female catkins are ovoid, when mature in autumn 10–22 millimetres (0.39–0.87 in) long and 7–10 millimetres (0.28–0.39 in) broad, on a 1–10 millimetres (0.039–0.394 in) stem, superficially resembling a small conifer cone. The small winged seeds disperse through the winter, leaving the old woody, blackish 'cones' on the tree for up to a year after. The white alder is closely related to the red alder (Alnus rubra), differing in the leaf margins being flat, not curled under. Like other alders, it is able to fix nitrogen, and tolerates infertile soils.

Some Plateau Indian tribes use white alder for female health treatment needs. Alder-bark tea was reportedly used by some California indigenous people for medicinal purposes.