White Alder
Alnus rhombifolia
White Alder is a medium-sized tree growing 15-25 meters (rarely 35 meters) tall. The tall, straight trunk is covered in smooth pale gray bark that becomes scaled with age. The trunk opens into a rounded crown of shiny, dark green leaves. The wide elliptical or rhombic leaves grow in an alternate pattern. The finely serrated leaves are 4-10 cm long and 2-5 cm wide. Especially when they are younger, the thin leaves have a sticky underside. The flowers are produced on dioecious catkins. The slender, yellow male catkins — 3 to 10 cm long — are produced in clusters of 2-7. The black, cone-like female catkins are 10-22 mm long and 7-10 mm wide. The small seeds stored in female catkins are dispersed via wind in the winter, carried by small wings.
Basic Information
Member of the Betulaceae, or birch, family
Closely related to the red alder (Alnus rubra)
Deciduous
Average lifespan of 100 years
Fast-growing in youth; the tree quickly grows to about 20 feet before slowing down
Habitat
Native to western North America, from British Columbia south to San Diego, California and east to western Montana
Commonly found in riparian habitats, such as along steam banks and wetlands, adjacent to chaparral, redwood forest, pine forest, and foothill woodland ecosystems
Ecological Role
Like other alders, white alder is able to fix nitrogen, which helps revitalize the soil
Bacteria in their roots move nitrogen from the air to the soil, making it available to the tree and nearby plants
Pine siskins eat seeds
Mule deer eat twigs, leaves and buds
Beavers eat their bark and build their dams and lodges
Host plant for the Western Tiger Swallowtail butterfly
Reproduction
Blooms from September-November
Monoecious, with male and female flowers on the same tree
The male catkins are produced in spring, prior to the leaves
The female catkins mature in fall
Alternative Names
California alder
Historical Uses
The inner bark had a number of uses including:
Fresh inner bark is an emetic
decoction (tea) of dried bark used for diarrhea, hemorrhaging, stomach aches, and to help with birth
Used as an astringent and antimicrobial to clean skin
Juice was used as a reddish dye by the Ohlone, Karok, Wailaki, and Mendocino Indians
