Oregon State University
Alphabetical List of Tree Common Names Alphabetical List of Tree Scientific Names Identification Key Mystery Tree

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Alder (Alnus)

  • Alternate, egg-shaped leaves with serrated or doubly serrated margins
  • Small woody cones about 1" long
  • Commonly found in moist areas next to water


Alders like moist surroundings and there are few creeks in western Oregon not overhung by them. Their peculiar woody cones (called strobiles) identify alders as surely as a flat tail identifies a beaver. They hang from the tree throughout winter like miniature lanterns. Alder leaves are shed while still green. Alders add nitrogen to the soil in the manner of legumes, and decomposing alder leaves improve soil structure.

Eight species of alder are native to North America; Oregon has four: red, white, Sitka, and thinleaf, but only two commonly reach tree size - and only red alder is abundant. Knowing their ranges and leaf traits will help in separating one species from another.


Large tree:(40'-80' tall; single trunk)

red alder: look for leaf margins that are tightly rolled under.

white alder: leaf margins are not rolled under.

Shrub or small tree: (under 25' tall; multiple trunks)

Sitka alder: leaf margins have very fine serrations; margins not rolled under.
This species will not be described further.

thinleaf alder: leaf margins have a double set of coarse teeth; margins not rolled under. This species will not be described further.


For more information on the alders native to the Pacific Northwest, go to the species page or see "Trees to Know in Oregon".

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