Northern Ontario Plant Database
Betula pumila L.
En: bog birch, dwarf birch, low birch, swamp birch, scrub birch
Betulaceae (Birch Family)
Images 2 and 3 of Betula pumila courtesy of the John Maunder and the Newfoundland Museum's Digital Flora of Newfoundland and Labrador.
General: A low to tall, deciduous shrub, 0.5–4 m tall. Young branches downy to smooth, twigs sometimes bearing scattered resin glands, but not warty-glandular as in Betula glandulosa (resin birch).
Leaves: Alternate, simple, firm, pinnately-veined, short petiolate. Leaf blades obovate, less commonly elliptic to orbicular; usually 2.5–5 cm long, 1–5 cm wide; yellowish-green to dark green above, paler beneath and smooth (glabrous) to very hairy; the base tapering (cuneate) to rounded; apex rounded to obtuse; and margins toothed (serrate to dentate), with broader teeth toward the tip; leaves with 2–6 pairs of lateral veins. More northerly populations, which have slightly hairy, glandular-dotted leaves, are often described as var. glandulifera, while the more southerly var. pumila has typically hairy leaves and lacks resinous glands (FNA, vol. 3:528).
Flowers: Unisexual, arranged in catkins (aments), with male and female catkins borne on the same shrub (plants monoecious). Male catkins small, pendant; female catkins cylindrical, erect, to 1.5 cm long; male and female flowers subtended by 3-lobed scales.
Fruit: Small winged samaras, with the wings slightly narrower than the body of the samara; seed-bearing catkins 0.7–3 cm long, erect, sessile; scales of the catkins shed with the fruit.
Habitat and Range: Bogs, wooded acidic or calcareous swamps, northern wetlands. Betula pumila is a boreal North American species that occurs throughout Ontario.
Similar Species: The dwarf resin birch, Betula glandulosa, a more arctic species, also has small obovate to nearly orbicular leaves, but the leaves of B. glandulosa are rarely longer than 1–2 cm long and their glabrous twigs bear large, resinous glands that give the twigs a warty appearance. In Ontario, Betula glandulosa is restricted to the Hudson Bay Lowlands, where it can hybridize with Betula pumila, forming Betula xsargentii.
Back to species list