A tree usually 40 to 50 ft, sometimes 80 ft high (Sargent), with a trunk 3 ft 6 in. in diameter, and a narrow pyramidal head of rather pendulous branches; young shoots angled, not downy; winter buds stalked, resinous. Leaves ovate or oval, 3 to 6 in. long, 2 to 4 in. wide, rounded or broadly wedge-shaped at the base, pointed, the margins decurved and with numerous small lobes or large teeth, each again unequally toothed; nerves parallel, reddish, in ten to fifteen pairs; upper surface dark green, lower one pale or greyish, covered at first with down which mostly falls away except on the nerves; stalk 1⁄2 to 1 in. long. Male catkins 4 to 6 in. long, 1⁄4 in. wide, usually three to five in a cluster. Fruits 1⁄2 to 3⁄4 in. long, barrel-shaped, three to six together.
Native of western N. America from Alaska to California; introduced some time previous to 1880, since when it has been grown at Kew. There are three in the collection, the largest 52 × 41⁄2 ft (1967), and another in the Edinburgh Botanic Garden of about the same size. In Eire, there are good examples at Headfort, Co. Meath, and in the Glasnevin Botanic Garden, Dublin. It is a handsome and striking alder, both when in flower in March and when in full foliage later. Jepson observes that in some parts of California it forms ‘pure groves of great beauty in bottom lands near the sea’.