Alnus rubra Betulaceae
Red Alder, Oregon Alder
- 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 bacteria,
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
- 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
- rubra: Latin, red; inner bark is orange-red so wounds turn red.
- Oregon State Univ. campus: in planting between Peavy and Dryden halls.