Alnus

Jepson (2012) (APG System)
Order	Fagales
Family

Jepson (1993) (Cronquist System)
Order	Fagales
Family	Betulaceae

Alders are trees typical of watercourses and wet, boggy areas. They often grow in the flood zone of a creek on stabilized sand bars or on the lower banks.

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.

There are four species of Alnus in California. Alnus rhombifolia and A. rubra are found in the San Francisco Bay Area, while A. incana and A. viridis are found in northern California and in higher elevations.

Of the two species found in central California, Alnus rubra is more common along the coast while A. rhombifolia is more common inland.

Alnus (Alder)

Plant Relationships
	California Species:	Alnus rhombifolia Alnus rubra Alnus incana tenuifolia Alnus viridis sinuata	White alder Red alder Mountain alder Sitka alder
	Other Species:	Alnus rugosa Alnus serrulata	Speckled alder (E US) Hazel alder (E US)

Description
	Growth Forms:	Alders are trees.
	Branching:	Alternate branching
	Leaves:	The leaves are simple, with serrated margins. Alnus rubra have leaf margins that are tightly rolled under and have veins that are indented into the top side of the leaf. Alnus rhombifolia leaf margins are not rolled under, and their veins are only slightly indented, if at all.
	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.

Growing Conditions
	Natural Range and Habitat:	Alders, while found in California, are more typical of wetter and northern climates.
	Sun and Exposure:	These trees are somewhat shade tolerant, especially while young. They grow better in full sun.
	Soil and Moisture:	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.

Horticulture and Restoration
	Horticultural Comments:	These are medium sized trees that would make a great addition to the landscape if you have a location with abundant and reliable moisture in the summer.
	Restoration Projects:	Alders are often used in riparian restoration projects. They would be most appropriately placed in the flood zone, 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.

California Native
Plant Guide

California Native Plant Guide
Native Plant Genera

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