Hazel Alder

Hazel Alder

Alnus serrulata (Aiton) Willd.


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

Smooth Alder in Baltimore Co., Maryland (4/27/2020). (c) Peter M Martin, some rights reserved (<a rel='license' href='http://creativecommons.org/licenses/by-nc/4.0/'>CC BY-NC</a>).

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


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. In Maryland hazel alder is found throughout the state in moist areas along streams and flood plains. ³

File:Alnus serrulata range map.jpg

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


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


  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


Towson University