Alnus rubra
Common name:
Red Alder
Oregon Alder
Pronunciation:
AL-nus RU-bra
Family:
Betulaceae
Genus:
Type:
Broadleaf
Native to (or naturalized in) Oregon:
Yes
- 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. However, "...no know characteristics infallibly distinguishing twigs of the two species in winter" (Gilkey and Packard, 1962, p.21). Whereas Randall et. al (1998) observe that new twigs of A. rhambidolia are "slightly triangular in cross section....lenticels evident", those of A. rubra "are distinctky triangular in cross section...lenticels prominent'.
- rubra: Latin, red; inner bark is orange-red so wounds turn red.
- A cut-leaf red alder (Alnus rubra f. pinnatisecta) exists and is sometimes available in the nursery trade.
- Oregon State Univ. campus: in planting between Peavy and Dryden halls; east side Kearney Hall, 14th & Monroe Ave.
Click image to enlarge
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flower clusters (catkins), spring
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male catkins, near pollen release
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plant habit, summer
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plant habit, in a landscape
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shoot
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leaves
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leaf margin
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leaves, comparison
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leaf margin, comparison
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seed cone development
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bud, twig, branch, late summer
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spent cones, comparison
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trunk, bark
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twigs and buds, winter
