Speckled Alder – Alnus incana

Speckled Alder – Alnus incana ssp. rugosa
Family Betulaceae – Alder, Birch, Hornbeam
Speckled Alder is a deciduous, thicket-forming shrub to 20' tall. Grows best in full sun.

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Speckled Alder leaf and strobiles
Speckled Alder leaf and strobiles

Speckled Alder is a tall, deciduous, thicket-forming shrub or small tree, to 20' tall. Its leaves are dark green above, light yellow-green and pubescent underneath, ovate to elliptic in shape with doubly toothed and shallowly lobed edges. Bark thin and smooth with conspicuous orange lenticels, hence the common name "speckled". Flowers: Staminate (male) catkins 1½"-3½" long; Pistillate (female) catkins sessile, cylindrical, and only 3/16" long. Fruit is an oval nutlet borne in egg-shaped cones. Nutlets flat, slightly winged, about 3mm across.

Grows best in full sun, moist, nutrient-rich soil. Good choice for disturbed site rehabilitation and providing streambank stability and erosion control. The presence of nitrogen-fixing, symbiotic bacteria in its root nodules makes speckled alder valuable for soil conditioning, but a bit coarse for most home landscapes.

All of the alders associate symbiotically with species of the actinomycete Frankia, leading to the formation of nodules on the roots of the plants and the fixation of atmospheric nitrogen. Speckled alder provides winter cover for snowshoe hare. Moose, muskrats, beavers, cottontail rabbits, and snow-shoe hares feed on the twigs and foliage. Low preference white-tailed deer browse, avoided by moose in the Lake Superior region.

Thickets provide hiding cover to moose and white-tailed deer. Beavers build dams and lodges with speckled alder. Songbirds, including American Goldfinch, Pine Siskin, and Redpoll feed on the seeds. Woodcock and grouse eat the buds and catkins. Thickets provide drumming sites for woodcock and grouse [2].

Speckled Alder

Most common in the region surrounding the Great Lakes and the St. Lawrence, including east-cental Canada, the Maritimes, and the Northeast and Lake States. Grows primarily in moist lowlands, frequently bordering streams and lakes, common in swamps and the older zones of bogs. Frequently found in riparian, bog, and nutrient-rich swamp communities. Often dominates Black Spruce (Picea mariana), Jack Pine (Pinus banksiana), Tamarack (Larix laricina), White Cedar (Thuja occidentalis), and Birch/Aspen understories on nutrient-rich, mesic sites. Where range overlaps that of its close relative, Green Alder (Alnus crispa), it tends to be found on lowland sites and Green Alder on upland sites [2].

Speckled alder grows throughout Wisconsin in wet soils and full sun to very light shade. It is the namesake of a type of wetland known as "alder thicket". It is also found in or adjacent to sedge meadows, shrub carr and swamps, along streams and in roadside ditches. It sometimes aggressively colonizes cut-over northern conifer swamps, as appears to be the case in many dense alder stands along small streams in northern Wisconsin [3].

1. Speckled alder, Morton Arboretum acc. 204-97-1 photos by Bruce Marlin
2. United States Department of Agriculture NRCS Plant Fact Sheet 565
3. University of Wisconsin at Green Bay, Trees of Wisconsin, "speckled alder; tag alder"
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Family Betulaceae – Alder, Birch, Hornbeam
The birches have long been popular ornamental trees in North America, chiefly in the northern United States and Canada. Our specimens include river birch, Dahurian birch, paper birch, Arctic birch, Manchurian birch, Manchurian alder, downy birch, Japanese white birch, and 10 other species.
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