Black alder is a fast-growing, medium sized tree. Leaves are dark green, round, glossy, and toothed. Male flowers are long drooping catkins that develop in the fall and overwinter on the tree, while female flowers develop as smaller, rounder catkins in the spring. The female flowers eventually develop into round cone-like structures called strobile. As with all species in the genus Alnus, black alders are capable of fixing atmospheric nitrogen through symbiosis with nitrogen fixing bacteria, and as such are often planted in highly disturbed areas.
This particular black alder is aptly planted in front of Alderman Hall, and as of 2017, is the only example of this species on the University of Minnesota Twin Cities campus. Black alders have also been the subject of recent research by Dr. Peter Kennedy in the Department of Plant Biology examining the “co-invasion” hypothesis of ectomycorrhizal fungi.
Black alders are currently considered to have potentially invasive traits, and are therefore not widely planted in managed landscapes. They are susceptible to numerous canker causing fungal pathogens, and this particular tree is often infested with wooly aphids.