Hazel Alder

Alnus serrulata (Aiton) Willd.

Description

Hazel alder, also called brookside alder ⁶, tag alder or smooth alder ¹, is a member of the birch family (Betulaceae). It is a small tree, seldom more than 20 tall. ² It has smooth bark (hence its other common name) and inconspicuous lenticels or pores. ¹ Leaves are oval, 2 to 4 inches long by 1.5 to 2.5 inches wide, with serrate or double-senate margins. Flowers are borne in catkins with separate male and female flowers on the same tree. The male catkins are 2 to 4 inches long, yellow and hang down in clusters of 2 to 5. ² Female catkins are less than 1 inch long, red and are erect. ² Fruits are cone-like, brown structures about 1 inch long that persist into the winter and bear numerous winged seeds. ¹

Three rod-shaped male flowers hang down to the right from a gray and red branch that looks slightly fuzzy and dusted. The flowers are a pale orange-yellow with touches of purplish-red buds. On the left side of the male flowers are small purplish-red female flowers that look like thick nubs with sharp hairs all around it.

Erect red female catkins and drooping yellow male catkins of hazel alder in spring. Maryland Biodiversity Project, S. Muller ³

Aged, dark brown female fruits of a Hazel Adler hanging from a leafy branch. Blurred branches of a Hazel Adler are behind it. — Dark brown, aged female fruits of a Hazel Alder hang from their branch with three leaves sprouted on an adjacent branch, with blurred Hazel Alder branches visible in the background.

Female fruits of previous year. Maryland Biodiversity Project, P. Martin ³

Distribution

Hazel alder is distributed from the Saint Laurence River system to the Great Lakes and South to Texas and Florida. It is found in wetlands. ⁴ In Maryland hazel alder is found throughout the state in moist areas along streams and flood plains. ³

Native range of hazel alder. Wikimedia Commons ⁵

Wildlife Importance

Numerous insects feed upon hazel alder including the flea beetle, leaf beetle, and leaf hoppers. ⁶ Numerous birds consume seeds and/or buds including American Wigen, Red-breasted Grosbeak, and Pine Siskin. ⁶ American beaver utilize the wood and bark for food and stems for dam construction. ⁶

Economic Importance

Hazel alder is used for stream bank stabilization. ⁷

Threats

Hazel alder is susceptible to canker and powdery mildew. ¹

Interesting Facts

Root nodules of hazel alder fix nitrogen ², one of only a new non-luminous plants that have this ability.
Native Americans had numerous uses of hazel alder including to reduce the pain of childbirth, for coughs and fevers and to lower blood pressure. ⁴
In earlier works Alnus serrulata was mistakenly called Alnus rugosa, a name that has unfortunately persisted. ⁴

References

Contributed by J. Hull

Towson University Glen Arboretum