Speckled Alder

Speckled Alder

Alnus incana ssp. rugosa (Du Roi) R.T. Clausen

Description

Speckled alder is in the birch family (Betulaceae) and is a subspecies separated from the introduced gray alder and native thin-leaf alder ¹.  It is a shrub or small tree that grows to 30 feet ².  The red, brown or gray bark is thin and smooth with conspicuous white lenticels that give it the common name ².  The oval leaves are up to 4 inches long with doubly serrate margins and straight, parallel veins from midrib to margin ².  Male and female flowers are in catkins.  The male catkins are up to 2.5 inches long at the end of the winter branches.  The female catkins are 3/4 inch cone-like structures that may persist after shedding seeds ².

Close-up photo of two grayish-brown stems which run vertically from top to bottom of the image, each mottled with small grayish-white spots. A much thinner, greenish brown stem with a few small, pinnately veined leaves, is also in focus directly beside the main stems of the image, all set in front a background of grass and other wooded vegetation. A few blurry and out-of-focus green leaves sit in the bottom right hand corner of the photo.

Bark with lenticels of speckled alder.  S. Muller, Maryland Biodiversity Project ³

Green, egg-shaped and elliptic simple leaves with doubly serrated margins, prominently pinnately veined to the point where they looked ridged, are attached by short petioles to light gray branches. The background is a grassy area next to a light brown wooden deck, with both newer and more weathered boards visible.

Leaves of speckled alder. S. Muller, Maryland Biodiversity Project ³

A dark brown branch studded with whitish lenticels extends from the lower right corner of the image. Attached are a few deep green, egg-shaped and elliptic leaves, as well as both this year's greener male catkins, and last year's dark brown female catkins. The dark brown female catkins are small, speckled with light green spots, resembling tiny pine cones, and are attached to a much lighter gray branch by light brown stems. The light green and light yellow colored male catkins are longer and thinner than the female catkins, with brown studs, attached to the branch by light brown/tan stems. The background is a grassy area with some out-of-focus green and brown vegetation.
Gray Alder in Allegany Co., Maryland (10/4/2019).

Previous year’s brown female catkins and current years green male catkins of speckled alder.  M. Evans, Maryland Biodiversity Project ³

Distribution

Speckled alder crosses two-thirds of Canada to its eastern seaboard and south to Virginia and Illinois.  It is found in damp soils and along stream banks.  In Maryland it is only in the mountains of Garrett and Allegheny Counties ³

A black-and-white map of the United States and Canada, showing the native range of the speckled alder shaded in green. The green shaded areas include the mid-Atlantic and New England states from Virginia to Maine, the Great Lakes region including the states Minnesota, Iowa, and North Dakota, as well as all Canadian provinces from Saskatchewan east to Newfoundland, but excluding Nunavut.

Natural range of speckled alder.  USDA, Forest Service ¹

Wildlife Importance

Speckled alder provides habitats for moose, rabbits and deer.  In addition they provide food for beavers and the construction of lodges and dams². The seeds provide food for birds such as redpolls and grouse ².

Economic Importance

Speckled alder has no commercial importance.  It is used horticulturally in wet areas and helps with control of erosion ².

Threats

Few insects or diseases affect speckled alder ².  It is capable of res-touting from low-intensity fire, but can be killed by high-intensity fire ².

Interesting Facts

  • Indigenous People used ground up bumblebees and alder root for women in childbirth ².
  • The roots of speckled alder have nodules that contain nitrogen-fixing bacteria which enhance the soil surrounding them ².

References

  1. USDA, Forest Service–Fire Effects Information System: Alnus incana
  2. USDA NRCS Plant Guide: Speckled alder
  3. Maryland Biodiversity Project:  Gray alder

Contributed by J. Hull

Towson University Glen Arboretum

Towson University