Alnus rubra
Common name: 
Red Alder
Oregon Alder
AL-nus RU-bra
Native to (or naturalized in) Oregon: 
  • Broadleaf deciduous tree, generally 40-50 ft (12-15 m) tall, record trees over 100 ft (30 m), in the open a broadly conical shape with spreading branches, in the forest a straight trunk visible to a narrow, rounded crown.  Bark smooth, light gray, but usually almost white with lichens.  Twigs triangular or rounded in cross section, buds stalked, 2-3 pubescent scales.  Leaves alternate, simple, oval to rhombic, 7-13 cm long, tapered from the middle to both ends, 8-15 vein-pairs, dull dark green above, grayish and pubescent on veins below, margin coarsely toothed, rolled under (revolute).   Male (pollen) catkins in small clusters at stem tips, about 10-15 cm long at pollination.   Female flower catkins 9-12 mm long, visible in winter in small clusters below male catkins, mature seed catkins (cones) barrel-shaped, 12-25 mm long.
  • Sun.  Tolerates infertile soil because it forms an association with a small soil bacterium, Frankia, resulting in root nodules that transform the tree into a nitrogen fixer.  In the landscape, red alder is a favored host for tent caterpillars.
  • Hardy to USDA Zone 5         Native along the Pacific Coast from southeastern Alaska, British Columbia, Washington, Oregon, to southern California, also found in northern Idaho.
  • It is distinguished from White Alder (A. rhombifolia) which has leaves that are green to yellow-green above and paler green below, and margins that are finely serrated or doubly serrated and not revolute.
  • rubra: Latin, red; inner bark is orange-red so wounds turn red.
  • Oregon State Univ. campus: in planting between Peavy and Dryden halls; east side Kearney Hall, 14th & Monroe Ave.
Click image to enlarge
  • flower clusters (catkins), spring

    flower clusters (catkins), spring

  • male catkins, near pollen release

    male catkins, near pollen release

  • plant habit, summer

    plant habit, summer

  • plant habit, in a landscape

    plant habit, in a landscape

  • shoot


  • leaves


  • leaf margin

    leaf margin

  • leaves, comparison

    leaves, comparison

  • leaf margin, comparison

    leaf margin, comparison

  • seed cone development

    seed cone development

  • bud, twig, branch, late summer

    bud, twig, branch, late summer

  • spent cones, comparison

    spent cones, comparison

  • trunk, bark

    trunk, bark

  • twigs and buds, winter

    twigs and buds, winter