Alnus rhombifolia, the white alder, is an alder tree native to western North America, from British Columbia and Washington east to western Montana, southeast to the Sierra Nevada, and south through the Peninsular Ranges and the Colorado Desert oases in Southern California. It occurs in riparian zone habitats at an altitudes range of 100–2,400 meters (330–7,870 ft). Alnus rhombifolia is primarily found in the chaparral and woodlands, montane, and temperate forests ecoregions. It is a medium-sized deciduous tree growing to 15–25 meters (49–82 ft) (rarely to 35 meters (115 ft)) tall, with pale gray bark, smooth on young trees, becoming scaly on old trees.
The flowers are produced in catkins. The male catkins are pendulous, slender, 3–10 centimeters (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. 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 (Wikipedia).