Alnus incana subsp. tenuifolia
Common name: 
Thinleaf Alder
Mountain Alder
AL-nus in-KAH-na ten-U-i-fol-i-a
Alnus tenuifolia
Native to (or naturalized in) Oregon: 
  • Broadleaf deciduous, thicket forming multistemmed shrub or small tree, to 20-40 ft (6-12 m), rounded form.   The bark is thin, smooth, and green-gray, grayish-brown, or reddish-brown; buds stalked or sessile.  Leaves alternate, simple, broadly elliptic or ovate-oblong, mostly 3-7 cm long, dull green on both sides, with doubly dentate margins, thinner and smoother than Sitka Alder.
  • Sun part shade.
  • Hardy to USDA Zone 5         Widely distributed, its native range is western North America, from central Alaska and the Yukon Territory, southeast to western Saskatchewan and British Columbia, and south throughout the Mountain States to New Mexico and California.  Considered the most common alder of the Rocky Mountains, the Sierra Nevada, and the east side of the Cascades.  It is often found near water, and its presence is an indication of streams, springs, or seeps.  Thinleaf Alder resembles, but is larger than, Speckled Alder (A. incana subsp. rugosa), with which it hybridizes where their ranges overlap.
  • Thinleaf Alder is part of a very large circumpolar alder group (Alnus incana, Gray Alder) which is distributed across much of North America and Europe.  Alnus incana has been separated into three subspecies, the Thinleaf Alder (A. incana subsp. tenuifolia), Speckled Alder (A. incana subsp. rugosa), both native to North America, and the third, A. incana subsp. incana, encompassing plants of the old world.  This classification system is not fully accepted.
  • From Flora of North America
    • ​Alnus incana subsp. rugosa (Speckled Alder):  Leaf blade thick, major teeth sharp; large shrubs
    • Alnus incana subsp. tenuifolia (Thinleaf Alder): Leaf blade thin and papery, secondary teeth rounded or blunt; large shrubs or small trees
  • incana: quite gray, a reference to the underside of leaves.  tenuifolia, tenui, slender, thin; folia, leaves
  • Oregon State Univ. campus: south of Peavy Hall, native plants area.


Click image to enlarge
  • plant habit

    plant habit

  • leaves


  • leaf


  • leaves and margin

    leaves and margin