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Western Wetland Flora

Field Office Guide to Plant Species

Thin-leaf Alder
Alnus tenuifolia Nutt.

JPG -- Species Photo JPG -- Distribution Map

Family: Birch (Betulaceae)
Flowering: April-June
Field Marks: This usually shrubby alder is distinguished by its doubly toothed and sometimes lobed leaves that are rounded or heart-shaped at the base.
Habitat: Moist woods, along streams, mountain meadows.
Habit: Shrub or rarely a small tree up to 20 feet tall.
Twigs: Smooth, but with conspicuous white lenticels.
Bark: Smooth, gray or reddish brown.
Leaves: Alternate, simple, ovate to oblong, up to 4 inches long, pointed or rounded at the tip, rounded or heart-shaped at the base, doubly toothed and sometimes shallowly lobed, paler on the lower surface, with hairy veins.
Flowers: Male and female flowers borne separately but on the same plant; male spikes slender, drooping, up to 3 inches long; female spikes upright, up to 1/2 inch long; flowers open before the leaves unfold.
Sepals: 4 in the male flowers, 0 in the female.
Petals: 0.
Stamens: 4, attached to the base of the sepals.
Pistils: Ovary apparently superior.
Fruits: Nutlets up to 1/8 inch wide, with a narrow, membranaceous wing, borne in a woody "cone."
Notes: Thin-leaf alder is sometimes known as Alnus incana ssp. tenuifolia.

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