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 to have some fine hair but do have small scattered resinous glands not large warty glands.
The leaves are alternate, very variable, stiff, elliptic to broadly ovate, widest above the middle, with 2 to 6 pairs of lateral veins and short-stalked. 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 tree is monoecious, that is with separate male and female flowers. Male catkins form in the fall and overwinter; then they expand in the spring with or just before leaf development; they are pendant, cylindric, 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 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.
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.
Above: A twig with the female aments. Drawing from Britton, N.L., and A. Brown. 1913. An illustrated flora of the northern United States, Canada and the British Possessions. 3 vols. Charles Scribner's Sons, New York. Vol. 1.
Below: Leaf upper side and paler underside. Older twig.
Below: Spring buds with fine hair on the twig. An older stem with whitish lenticels. A female ament.
Below: A comparison of leaves of the five Birch species described on this site.
Notes: Bog Birch is indigenous to the Garden, Eloise Butler noted it in her log on April 29, 1907. It has been present since that time. It is a plant of the northern forests, being found in the U.S. in the northern tier of states and in most of Canada. In Minnesota it is present in almost all the counties except those of the drier SW quadrant
Eight species of birch are recorded from surveys in Minnesota. Three of them are crosses formerly reported but there are no known populations. The other five are native and are: B. alleghaniensis, Yellow Birch; B. cordifolia, Heart-leaved Birch; B. nigra, River Birch; B. papyrifera, Paper Birch; and B. pumila, Bog Birch. All but B. cordifolia are in the Garden.
References: Plant characteristics are generally from sources 1A, 32, W2, W3, W7 & W8 plus others as specifically applied. Distribution principally from W1, W2 and 28C. Planting history generally from 1, 4 & 4a. Other sources by specific reference. See Reference List for details.
Friends of the Wild Flower Garden, Inc. Text and photos are by G. D. Bebeau unless otherwise credited. "www.friendsofthewildflowergarden.org"