A. rhombifolia generally occurs in thickets or as individuals on riparian sites in mid-elevation conifer forests and montane fir forest.
White alder is a good indicator of the presence of flowing surface water.
Its bark is lightly colored and fissured into flat scaly ridges. The branches tend to form a spreading canopy. The female flowers are borne in reddish, cone-like catkins less than 1 inch in length. Cones occur on short stalks in clusters of 3-7. Male flowers are 4 to 6 inch yellow drooping catkins.