The Plants of Michigan

Betulaceae, the Birch Family

Trees or shrubs with alternate simple leaves and inconspicuous monoecious flowers, the staminate flowers in catkins, and the pistillate in catkins or small clusters.

1a. Trees, with white or yellowish bark exfoliating in thin papery plates or scales — 2.
1b. Tree or shrub, with smooth, dark gray bark; trunk fluted with prominent longitudinal ridges	Hornbeam, Carpinus caroliniana.
1c. Trees or shrubs; the bark more or less roughened, but not exfoliating; trunk not fluted — 3.
2a. Bark white or chalky	Paper Birch, Betula alba var. papyrifera.
2b. Bark yellowish	Yellow Birch, Betula lutea.
3a. Shrubs, with leaves 4 cm. long or less — 4.
3b. Shrubs or trees, with leaves 5 cm. long or more — 5.
4a. Twigs glandular-warty	Dwarf Birch, Betula glandulosa.
4b. Twigs not glandular	Swamp Birch, Betula pumila.
5a. Twigs and bark with the odor of wintergreen	Sweet Birch, Betula lenta.
5b. Twigs and bark without odor of wintergreen — 6.
6a. Fruit clusters woody, persistent on the plant for a long time — 7.
6b. Fruit clusters herbaceous, dropping in late autumn — 9.
7a. Leaves rusty or whitish beneath, and pubescent at least on the veins	Speckled Alder, Alnus incana.
7b. Leaves green beneath, and either pubescent or smooth — 8.
8a. Leaves broadest at or below the middle	Mountain Alder, Alnus crispa.
8b. Leaves broadest above the middle	Smooth Alder, Alnus rugosa.
9a. Tree; fruit a cluster of bladder-like sacs each containing a small achene	Ironwood, Ostrya virginiana.
9b. Shrubs; fruit a nut within a close-fitting involucre — 10.
10a. Involucre of 2 broad bracts, almost separate and not much longer than the fruit	Hazel, Corylus americana.
10b. Involucre of united bracts, prolonged into a bristly beak beyond the fruit	Beaked Hazel, Corylus rostrata.