Tag alder is a multi-stemmed deciduous shrub with brownish gray bark. The leaves alternate along the twigs and are simple, oval, and doubly serrated (toothed). The leaves are 2 to 4 in long, dull dark green above, paler and may be velvety below, with prominent, parallel veins. Each shrub produces both both male and female flowers called catkins. The male catkins are green and can be up to 2.5 in long. The female flowers are about 0.5 in long and develop into cone-like fruits that release the seeds. These cones often persist through the winter. Tag alder flowers bloom between March and April and fruits become ripe later in the summer.
Tag alder, also known as hazel or smooth alder, is commonly found in wetland areas. Because this shrub does well in wet habitats, it is often used for stream restoration and bank stabilization projects. This shrub also provides important habitat for Woodcock, a woodland game bird. Tag alder shrubs are also nitrogen fixers (like many legumes) and can enrich the nitrogen in the soil where they grow.