A large single to multistemmed tree commonly found growing in wet ground. Bacterial nodules on the roots of alders fix atmospheric nitrogen. Flowers early spring. Male flowers are catkins, very profuse pollen; female flowers are small, red, and insignificant, on a swollen green bulb. Similar to Italian Alder which is often grown in plantations - native alder has more rounded leaves, browner bark, and is more inclined to be multistemmed. Leaves are distinctly asymmetrical, lopsided even.
Pollen grains are distinctive rounded heptangular or less usually quadrangular. When fresh the internal cytoplasm forms distinct arcs between adjacent pores. Five, or four, large and clear pores, one on each apex of the grain. About 25-30 microns across.