Trees and Shrubs of the Eloise Butler Wildflower Garden

Bog Birch is a native perennial shrub, that has an erect but coarse growth pattern forming an irregular to spreading shape of 4 to 13 feet in height, but in extreme northern areas may be less than a foot tall.

Twigs and stems are a reddish-gray to reddish-brown with whitish lenticels and thin bark that does not ex-foliate. The twigs do not have an odor or taste of wintergreen like some birches do; they can be smooth or have some fine hair and do have small scattered resinous glands but not large warty glands.

The leaves are alternate, short-stalked, very variable, stiff, elliptic to broadly ovate, widest above the middle, with 2 to 6 pairs of lateral veins. The margins are coarsely toothed, the tip is broadly pointed to rounded, the base tapered to rounded. The underside is a paler color and may be smooth to having many short soft hairs. The leaves often have small resinous glands but these may be absent.

The inflorescences are male catkins and female aments.

Flowers: The shrub is monoecious, that is with separate male and female flowers, but on the same plant. Male catkins form in the fall and overwinter; then they expand in the spring with or just before leaf development; they are pendant, cylindric, 0.4 to 1.0 inches long. The individual flowers are only 1/8 inch long, are in clusters of 3 per scale on the catkin. Female flowers appear before the leaves are fully expanded and are on greenish upright aments, about 0.3 to 0.8 inches long, back of the tip on the same twigs. They have an ovary, a pair of styles but no calyx or petals. Like the male flowers, they are in clusters of 3 on the ament and obscured by the bracts (scales).

Fruit: Pollination is by wind - plants are not self-fertile. Female flowers mature inside the ament which becomes an upright cylindrical non-woody cone, brownish in color. The bracts become dry scales at maturity, each scale having three lobes and three narrow-winged single seeds (samaras) attached; of which there are 30 to 50 per cone and which disperse by wind and water in late autumn and winter. Of the three lobes of the scales, the two laterals are shorter but broader than the longer narrower central lobe.

Varieties: Two varieties are sometimes listed as var. pumila and var. glandulifera, with the differences in specimens with glands and hair on leaves being the determining factor; however Flora of North America treats these as just normal variations within the species and does not accept these varieties.

Habitat: Bog Birch grows in sunny moist to wet areas, bogs, fens, swamps and riparian edges where it adapts to sandy soils. It is not tolerant of shade. Bog Birch reproduces by seed dispersal and vegetatively by branch layering, sprouting from dormant buds on the root crown, and by rhizomes. In northern areas it propagates extensively by rhizomes forming clonal colonies. The species frequently hybridizes.

Names: The genus, Betula, is the Latin word for the birch tree. The species, pumila, means 'dwarf' referring to the small size of this species. The author name for the plant classification, 'L.' refers to Carl Linnaeus (1707-1778), Swedish botanist and the developer of the binomial nomenclature of modern taxonomy.

Comparisons: One other Betula species is similar but normally found only in the northern part of the ranges - B. glandulosa, the Resin Birch, where the twigs have large resinous glands giving them a warty appearance.