Photo © Robert Moseley CLICK PHOTO FOR A LARGER IMAGE

Betula pumila L.

Swamp Birch; Dwarf Birch

Betulaceae (Birch family)

Synonym: Betula pumila L. var. glandulifera Regel

General Description: Shrubs with many erect stems up to about 4 m tall emanating from the base, and with dark reddish-brown bark. The small obovate, elliptic, or nearly orbicular leaves have numerous small teeth along the margin. Twigs have small, scattered resinous glands, especially near the nodes. Plants are monoecious with elongated staminate catkins, and pistillate catkins that terminate the short lateral branches (spur shoots) of the season. The fruit is a small, cylindrical, papery "cone". It is comprised of many small winged fruits (samaras) that scatter when the "cone" falls apart at maturity. The samara's wings are slightly narrower than the body and broadest near the center.

Field Identification Tips: The distinctive leaf shape, reddish-brown bark, and resinous twigs are usually enough to differentiate this shrub from all other birches except for Betula glandulosa, which takes more careful examination to distinguish.

Phenology: Pistillate catkins flower in the spring.

Similar Species: Most likely to be confused with B. glandulosa (bog birch). Betula pumila is recognized by its samara (fruit) wings being more than half as broad as the body, the more or less obovate leaves with more than 10 teeth on each side, and taller stature, up to about 4 m tall. Betula glandulosa has narrow samara wings less than half as broad as the body, broadly ovate to orbicular leaves with fewer than 10 teeth on each side, and a stature of usually less than 2 m tall. Size is the easiest way to tell the two apart, with most individuals in a stand of B. pumila being greater than 2.5 m tall.

Photo © Robert Moseley CLICK PHOTO FOR A LARGER IMAGE

Habitat: Bogs, fens, swamps, and lakeshores.

Global Distribution: Across most of Canada, extending southward into the Northeastern, Great Lake, and Pacific Northwest states. It also is known from Colorado and adjacent portions of Nebraska, Kansas, and Wyoming.

Idaho Distribution: The Kootenai and Moyie river drainages in Boundary County and the Priest Lake area in Bonner County.

References:

Brayshaw, T. C. 1976. Catkin bearing plants (Amentiferae) of British Columbia. Occasional Papers of the British Columbia Provincial Museum No. 18. Victoria, BC: Department of Provincial Secretary. 176 pp.

Flora of North America Editorial Committee. 1997. Flora of North America. Vol. 3, Magnoliophyta: Magnoliidae and Hamamelidae. Oxford University Press, New York. 590 pp.

Johnson, F. 1995. Wild trees of Idaho. University of Idaho Press, Moscow, Idaho. 212 pp.

Moseley, R. K. 1989. Field investigations of 16 rare plant taxa occurring in wetlands on the Bonners Ferry Ranger District, Idaho Panhandle National Forest. Report prepared for the Panhandle National Forests by the Idaho Department of Fish and Game, Conservation Data Center, Boise. 75 pp. plus appendices.