A small tree or shrub. Leaves: ovate, acuminate, obtuse or crenate at the base. Flowers: aments of both kinds on long, slender peduncles.

The Mountain Alder has rather dark bark, and bright green leaves, which are doubly toothed, thin, and very gummy when young. The staminate aments are pendulous, like catkins, and the pistillate ones are rounded and erect.

Alnus sitchcnsis, or Speckled Alder, has brown bark, and broader leaves than the preceding species, these leaves are acutely doubly-toothed, light green on both sides, and speckled with white. This tree grows in wet places.