Description

Description:

This tree, formerly known as Alnus oregona, grows in riparian zones. They usually grow in the floodplain of a creek on stabilized sand bars or on the lower banks.

They usually grow to 50 ft, but can reach 75 ft.

Branching:

Alternate branching.

Leaves:

The deciduous leaves are oblong-ovate, with serrated margins. They are distinguished by A. rhombifolia by their leaf margins, which are tightly curled under, and by their veins, which are deeply indented into the leaf.

Flowers:

The flowers are in catkins, which emerge and open in mid-winter

Fruit:

The seeds are borne in small cones, similar to pine cones, but much smaller. The cones are found at the tips of the branches. The seed ripens in mid to late fall.

Plant Relationships

Related California Species:

Alnus rhombifolia
Alnus incana tenuifolia
Alnus viridis sinuata

White alder
Mountain alder
Sitka alder

Related Exotic Species:

Alnus rugosa
Alnus serrulata

Speckled alder (E US)
Hazel alder (E US)

Growing Conditions

Natural Range and Habitat:

Alnus rubra is found in riparian zones in northern California, especially near the coast. We are near the southern extent of its range, which extends northward in the coast range almost to Alaska..

Sun and Exposure:

Red alder is somewhat shade tolerant when young. It grows best in full sun.

Soil and Moisture Requirements:

Alders are found in the flood zones of creeks. They may also be found in wet and boggy sites. They will grow in a variety of soils, but tend to be found on sandier sites.
Red alder is tolerant of somewhat brackish soil conditions. This is particularly noticable in protected areas along the coast where they grow in moist soils just above the high tide line.

Horticulture and Restoration

Wildlife Habitat:

Restoration:

Alnus rhombifolia is not used often in restoration, because there are only rare occasions when someone is restoring a wooded marsh or riparian zone directly along the coast. They would be, however, successful trees where they are used.

Alders would be most appropriately placed in the floodplain, but few restoration professionals would do that, because they are correctly concerned that the trees will be swept away in the current before they have a chance to root.

The solution, however, is to place them on an upper bank, out of danger. However, the trees are now in unfavorable growing conditions where they often perform poorly.

Uses in Landscaping:

These are very attractive trees, with straight limbs that have a stiff, yet elegant appearance. When placed in the right location, they grow vigorously. Their main limit to landscaping and restoration is their requirement for moist sites.

Horticultural Comments:

Sunset zones 4-6, 15-17

Cronquist System

Order:

Fagales

Family:

Betulaceae

Genus:

Alnus

APG System

Order:

Fagales

Family:

Betulaceae

Genus:

Alnus