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White Alder
Alnus rhombifolia
About White Alder (Alnus rhombifolia) Nurseries Show All Photos White Alder is a member of the Birch family (Betulaceae) native to western North America, from Washington east to western Montana and south to San Diego County, occurring at altitudes of 100-2400 meters. It has not been reported from northern Baja California but has been predicted to occur there on the basis of its climatic adaptation. It is a medium-sized deciduous tree growing to 15-25 meters (rarely to 35 meters) tall, with pale gray bark, smooth on young trees, becoming scaly on old trees. The leaves are alternate, rhombic to narrow elliptic, 4-10 centimeters long and 2-5 centimeters broad, with a finely serrated margin and a rounded to acute tip; they are thinly hairy below. The flowers are produced in catkins. The male catkins are pendulous, slender, 3-10 centimeter long, yellowish, and produced in clusters of two to seven; pollination is in early spring, before the leaves emerge. The tree produces very large amounts of pollen at this time. The female catkins are ovoid, when mature in autumn 10-22 millimeter long and 7-10 millimeter broad, on a 1-10 millimeter stem, superficially resembling a small conifer cone. The small winged seeds disperse through the winter, leaving the old woody, blackish 'cones' on the tree for up to a year after.

Plant White Alders in moist soils, or on the edges of permanently wet areas, such as streambanks or at the edge of a regularly irrigated area. They grow quickly to 20 feet, and then slowly to 50 feet. The roots can be invasive so use caution in deciding where to plant it. Due to its ultimate size, it may not be appropriate for small residential gardens.
Plant Description
Plant Type

Max. Height
49.2 - 82 ft (15 - 25 m)

Max. Width
35 ft (10.7 m)

Upright, Rounded, Upright Columnar

Fragrant - Pleasant

Growth Rate

Winter Deciduous

Flower Color
Green, Cream

Flowering Season
Summer, Fall

Native Status

Natural Setting
Site Type
Usually found in wetland such as permanent stream edges, often adjacent to other vegetation such as chaparral, redwood forest, pine forest, and foothill woodland

Sun, Part Shade

Elevation ?
-7' - 10807'

Annual Precip. ?
4.8" - 153.6"

Summer Precip. ?
0.14" - 5.72"

Coldest Month ?
23.6° F - 59.1° F

Hottest Month ?
44.8° F - 87.7° F

Humidity ?
0.02 vpd - 38.56 vpd

Soil Description
Tolerant of sand and clay

Soil PH
4.0 - 8.0

Fast, Medium, Slow

Sunset Zones ?
1*, 2*, 3*, 4, 5, 6, 7*, 8, 9*, 10, 14*, 15*, 16*, 17*, 18*, 19, 22*, 23*, 24*

Companion Plants
Wetland-riparian trees and plants including Maples (Acer species), Dogwood (Cornus species), Ash (Fraxinus species), Walnut (Juglans species), Western Sycamore (Platanus racemosa), Cottonwood (Populus species), Willow (Salix species), Spicebush (Calycanthus occidentalis), Wild Honeysuckle (Lonicera species), Wild Azalea (Rhododendron species), Wild Currant (Ribes species), Wild Rose (Rosa species), and Wild Grape (Vitis species)

Landscaping Information
Water Requirement ?
Moderate - High
Extremely Low
Very Low
Moderate - High

Moderately Popular

Max. Summer Water ?
Keep moist
No Summer Water
Keep moist

Common uses
Bird Gardens, Butterfly Gardens

Nursery Availability
Commonly Available

Sources include: Wikipedia. All text shown in the "About" section of these pages is available under the Creative Commons Attribution-ShareAlike License. Plant observation data provided by the participants of the California Consortia of Herbaria, Sunset information provided by Jepson Flora Project. Propogation from seed information provided by the Santa Barbara Botanical Garden from "Seed Propagation of Native California Plants" by Dara E. Emery. Sources of plant photos include CalPhotos, Wikimedia Commons, and independent plant photographers who have agreed to share their images with Calscape. Other general sources of information include Calflora, CNPS Manual of Vegetation Online, Jepson Flora Project, Las Pilitas, Theodore Payne, Tree of Life, The Xerces Society, and information provided by CNPS volunteer editors, with special thanks to Don Rideout. Climate data used in creation of plant range maps is from PRISM Climate Group, Oregon State University, using 30 year (1981-2010) annual "normals" at an 800 meter spatial resolution.

Links:   Jepson eFlora Taxon Page  CalPhotos  Wikipedia  Calflora

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