Trees or shrubs with monoecious flowers, both sorts in catkins, 2 or 3 flowers under each scale or bract of the catkin. Ovary 2-celled and 2-ovuled, but in fruit only 1-celled and 1-seeded. Fruit a small nut. Stigmas 2, long and slender. Twigs and leaves often aromatic.
1. Bet'ula. Sterile'catkins long and pendulous, formed during summer and expanding the following spring; each flower consisting of one small scale to which is attached 4 short filaments; S flowers under each scale of the catkin. Fertile catkins stout, oblong, the scales or bracts 5-lobed and with 2 or 3 flowers under each; each flower a naked ovary, becoming a winged nutlet in fruit. Bark easily coming off in sheets.
2. AInus. Catkins much as in Betula, but each fertile and sterile flower has a distinct 8-5-parted calyx. Catkins solitary or clustered at the ends of leafless branchlets or peduncles. Nutlets wingless or nearly so.
(These two genera are included in Cupuliferse in Macoun's Catalogue.)
1. B. lenta, L. (Cherry-Birch, Sweet or Black Birch.) Bark of the trunk dark brown, close, aromatic; that of the twigs bronze-coloured. "Wood rose-coloured. Leaves ovate, with somewhat heart-shaped base, doubly serrate, pointed, short-petioled. Fruiting catkins sessile, thick, oblong-cylindrical. - Moist woods.
2. B. lu'tea, Michx. (Yellow or Gray Birch.) Bark of the trunk yellowish-gray, somewhat silvery, scaling off in thin layers. Leaves hardly at all heart-shaped. Fruiting catkins thicker and shorter than in No. 1. - Moist woods.
3. B. populifo'lia, Ait. (American White Birch. Gray Birch.) Leaves very tremulous on slender petioles, triangular, very taper-pointed, nearly truncate at the base, smooth and shining except when young. Bark of trunk white, less separable than in Canoe Birch. - Poor soil, Atl. Prov.
4. B. papyra'cea, Ait. (B. papyrifera, Michx., in Macoun's Catalogue.) (Paper or Canoe Birch.) Bark of the trunk white, easily separating in sheets. Leaves ovate, taper-pointed, heart-shaped, long-petioled. Fruiting catkins cylindrical, usually hanging on slender peduncles. - Woods.
5. B. pu'mila, L. (Low Birch.) A shrub with brownish bark, not glandular. Leaves ovate or roundish, pale beneath; veinlets on both surfaces finely reticulated. Catkins mostly erect, on short peduncles. - Bogs and low grounds, northward.
1. A. inca'na, Willd. (Speckled or Hoary Alder.) A shrub or small tree, growing in thickets in low grounds along streams. Leaves oval or ovate, rounded at the base, serrate, whitish beneath. Flowers preceding the leaves in early spring, from clustered catkins formed the previous summer and remaining naked over winter. Fruit wingless.
2. A. vir'idis, DC. (Greek or Mountain Alder.) A shrub 3-8 feet high, along mountain streams. Flowers appearing with the leaves, the staminate catkins having remained naked during the winter, the pistillate enclosed in a scaly bud. Fruit with a thin wing. - Northward.