Green alder is a large spreading shrub, often forming thickets and occurring across North America; widely distributed from Alaska to Greenland. It is a close relative to the stika alder (Alnus viridus ssp. sinuata) and together these species span the Northern Hemisphere. Green alder is a short-lived 'nurse tree' or pioneer species following glacial retreat, landslides, or man made disturbances. Interestingly, it has a symbiotic relationship with microorganisms that can fix nitrogen from the air.

Leaves are shinny, yellowish green, ovate or broadly elliptic; finely toothed and possibly undulated. Smooth, dark reddish brown twigs are covered with light lenticels. Male and female flowers occur on the same tree and appear from April to May. Like other alders, the fruit is cone-like, starting yellow then turning brown.

The bark has been use medicinally by natives as an astringent, or for tanning leather and dying textiles. Green alder is ecologically valuable as a soil stabilizer for streambanks, as a windbreak, and to improve soil quality in nutrient poor sites.