Alnus incana subsp. tenuifolia

(Nuttall) Breitung

Amer. Midl. Naturalist 58: 25. 1957.

Common names: Thinleaf alder mountain alder
Basionym: Alnus tenuifolia Nuttall N. Amer. Sylv. 1: 48. 1842
Synonyms: Alnus incana var. occidentalis (Dippel) C. L. Hitchcock Alnus incana var. virescens S. Watson Alnus occidentalis Alnus rugosa var. occidentalis (Dippel) C. L. Hitchcock
Treatment appears in FNA Volume 3.

Shrubs or trees, to 12 m; shrubs ascending, open, spreading, trees small, shrubby. Bark light gray to dark brown, smooth; lenticels pale, orbiculate to elliptic. Winter buds nearly divergent, ellipsoid, 4–7 mm, apex obtuse; stalks 1–3 mm; scales 2, equal, valvate. Leaf blade ovate to elliptic, 4–10 × 2.5–8 cm, thin, base broadly cuneate to rounded, margins distinctly doubly serrate to nearly crenate or lobulate, teeth relatively blunt or rounded, apex acute to obtuse; surfaces abaxially glabrous to sparsely pubescent, slightly to not noticeably resin-coated. Inflorescences: staminate catkins in 1 or more clusters of 3–5, 4–10 cm; pistillate catkins in 1 or more clusters of 2–5. Infructescences ovoid, 1–2 × 0.8–1.3 cm; peduncles 1–5 mm. 2n = 28.

Phenology: Flowering early spring.
Habitat: Stream banks, lake shores, margins of wet fields and meadows, bog margins, and muskegs
Elevation: 100–3000 m


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Alta., B.C., N.W.T., Sask., Yukon, Alaska, Ariz., Calif., Colo., Idaho, Mont., Nev., N.Mex., Oreg., Utah, Wash., Wyo.


Alnus incana subsp. tenuifolia is somewhat more treelike than the eastern A. incana subsp. rugosa, from which it also differs in leaf shape, leaf margins, and other characters. It is a frequent component of streamside vegetation throughout the Rocky Mountains and other mountainous parts of western North America.

Native Americans used alnus incana subsp. tenuifolia medicinally for pains in the lungs or hips, for scrofula, as a laxative, and as a diuretic for gonorrhea (D. E. Moerman 1986).

Selected References


Lower Taxa

John J. Furlow +
(Nuttall) Breitung +
Alnus tenuifolia +
Thinleaf alder +  and mountain alder +
Alta. +, B.C. +, N.W.T. +, Sask. +, Yukon +, Alaska +, Ariz. +, Calif. +, Colo. +, Idaho +, Mont. +, Nev. +, N.Mex. +, Oreg. +, Utah +, Wash. +  and Wyo. +
100–3000 m +
Stream banks, lake shores, margins of wet fields and meadows, bog margins, and muskegs +
Flowering early spring. +
Amer. Midl. Naturalist +
Alnus incana var. occidentalis +, Alnus incana var. virescens +, Alnus occidentalis +  and Alnus rugosa var. occidentalis +
Alnus incana subsp. tenuifolia +
Alnus incana +
subspecies +