bog birch

LC - Least Concern

N5 - Secure

SNR - Unranked

not listed

OBL - Obligate wetland

OBL - Obligate wetland

OBL - Obligate wetland

Bog birch is common deciduous shrub. It is native across the northern half of North America. In the United States it occurs from Maine to Maryland west to Washington and northern California. It is common in Canada, Michigan, Wisconsin, and Minnesota., but in the U.S. it is uncommon wherever else it occurs. In Minnesota it is absent in the southwest, common elsewhere. It is found in wetlands, including calcareous fens, wooded swamps, and muskegs, and on stream sides and lake shores, and at the shrubby edges of sphagnum bogs. It grows under full or partial sun in moist or wet peaty soil or calcareous sand.

Bog birch is an erect, perennial shrub that rises on multiple stems from a shallow woody root system. It can be 3″ to 13″ (1 to 4 m) tall and 1¼″ (3 cm) in diameter at the base, but it is usually no more than 6″ in height.

The stems are erect or curve upward at the base (ascending). The bark on young stems and branches is thin, smooth, dark reddish-brown, and shiny, with scattered, small, pale, inconspicuous, horizontal, corky areas (lenticels). As it ages the bark on the trunk and lower branches becomes gray and slightly rough but does not peel.

Twigs are slender and dark reddish-brown. They have numerous spur shoots. They do not have a wintergreen odor or taste. In the first year they are usually moderately covered with non-glandular hairs, sometimes almost hairless, but always with some hairs. They also have scattered, small, resinous glands, especially near the nodes. The presence of both hairs and glands is the feature that some botanists use to identify this as var. glandulifera. Winter buds are slender, round in cross section, and sharply pointed. They are covered with smooth overlapping scales.

The leaves are borne on two distinct kinds of shoots. Long shoots are produced at the tip of the twig. They are fast growing and have well-spaced nodes. Spur shoots emerge from the widely-spaced leaf axils along the long shoot. They are very slow growing and have very little growth between nodes.

Two types of leaves are produced: early leaves, also called preformed leaves; and late leaves, also called neoformed leaves. Preformed leaves overwinter in the bud and are fully formed or almost fully formed before bud burst in the spring. They are the first leaves to mature in the spring. They are produced on spur shoots and at the base of long shoots. Neoformed leaves are all of the subsequent leaves produced on long shoots. They are formed from new tissue growing at the tip of the shoot in the season that they emerge.

The leaves are alternate, 1″ to 2″ (25 to 50 mm) long, and ⅝ to 1″ (15 to 25 mm) wide. They are borne in pairs on spur shoots and singly on long shoots. Each leaf is on a 1⁄32″ to ¼″ (1 to 7 mm) long leaf stalk (petiole). The petiole is light green to red and may be hairy or hairless. The leaf blade is somewhat thick, egg-shaped and widest above the middle (obovate), oval and broadest in the middle (elliptic), or nearly circular. It has just 2 to 6 pairs of lateral veins. It is heart-shaped to rounded at the base and broadly angled or rounded at the tip. The upper surface is dark green and hairless. The lower surface is pale green, hairless or slightly hairy, and has scattered sunken glands. The margins have 10 or fewer coarse teeth on each side.

Male and female flowers are borne on the same plant and on the same branch. The male catkin is preformed and emerges in the late summer the year before it sheds its pollen. A single catkin is held erect or ascending at the end of a leafless branchlet formed at the tip of a current year long shoot. It is stout, erect, and 3⁄16″ to ⅝″ (5 to 6 mm) long. It remains on the tree over the winter. When it opens the following spring it becomes brownish-yellow, spreading or pendant, and ¾″ to 1¼″ long.

The female catkin is also preformed but remains in the protective bud over the winter. In the spring a single catkin is held erect on a ⅛″ to ⅜″ (3 to 9 mm) long stalk (pedicel) at the end of a very short leafy branchlet. The catkin is green, stout, and short-cylindrical at first. When it flowers it becomes ⅜″ to 11⁄16″ (9 to 18 mm) long and reddish at the tip due to the red stigmas of the tiny flowers.

Fruits are contained in mature seed catkins. Each seed catkin is cone-like, cylinder-shaped, and 5⁄16″ to ¾″ long. It persists through at least part of the winter. The fruit is a tiny, two-winged nutlet (samara). The samara matures in mid-August to late September and is dispersed in the fall and early winter by wind and gravity.

3″ to 13″ (1 to 4 m)

Female catkins green and reddish

Moist to wet. Calcareous fens, wooded swamps, margins of sphagnum bogs, muskegs, stream sides, and lake shores,

Late mid-April to mid-May

Sources

2, 3, 4, 5, 7, 8, 28, 29, 30,

Native

Common in Minnesota

Some authorities recognize four varieties of Betula pumila. Of these, only B. p. var. glandulifera is common in Minnesota. There is just a single record of B. p. var. renifolia in the state. Most taxonomists do not recognize any varieties.