Green alder is a shrub with alternate, simple, finely toothed leaves. The winter leaf buds are not stalked and are covered by 3 or more imbricate outer scales, unlike speckled alder with stalked buds and 2 outer bud scales. The female aments (catkins) of green alder are covered by exterior bud scales, unlike speckled alder in which the aments are lacking the outer scales (naked buds). Green alder flowers open as the leaves unfold, much later than speckled alder in any given area and the single-seeded dry fruits (achenes) are winged.

Green Alder is much less common in Wisconsin than speckled alder, being relatively common mostly in the counties near Lake Superior. It appears to be more closely associated with banks and sandy shorelines rather than the low wet habitats of speckled alder. This species was long known as Alnus crispa in the Midwest and may be referenced under that name in many botanical books for the area.