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

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

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

1. North Carolina Extension:  Alnus serrulata
2. Missouri Botanical Gardens:  Alnus serrulata
3. Maryland Biodiversity Project; Smooth alder
4. Flora of North America:  Alnus serrulata
5. Wikimedia Commons: Alnus serrulata
6. Illinois Wildflowers:  Brookside alder
7. Plants for a Future: Alnus serrulata

Contributed by J. Hull

Towson University Glen Arboretum