Aromatic deciduous trees or shrubs. Twigs slender, terete; lenticels elongated horizontally (in this respect resembling cherry); pith minute, flattened, continuous, green. Buds moderate, solitary, fusiform-ovoid, sessile, with 2 or 3 visible scales. Leaf-scars alternate, oval, triangular or crescent-shaped; bundle-traces 3. Staminate catkins naked through winter, often 2 or 3 in a cluster; pistillate catkins ovoid or cylindrical.
Twigs with a sweet wintergreen fragrance
b. Bark on old trunks black; buds sharply
pointed, divergent, mostly glabrous; twigs brown to black, quite aromatic
b. Bark on old trunks bronze, scaly; buds appressed, at least along the lower half, often hairy;twigs greenish-brown somewhat aromatic
Twigs without a wintergreen fragrance
b. Bark on old trunks grayish-white, usually close; twigs gray, with prominent warty lenticels;buds short, taper ing both ways from the middle
b. Bark on old trunks exfoliating in thin strips; twigs brown to black; buds tapering from base to apex
c. Twigs and buds somewhat hairy; twigs reddish-brown;freshly exposed bark on old trunks salmon-pink or greenish-brown, the older dark.
c. Twigs and buds mostly glabrous; twigs nearly black; bark on old trunks chalky-white
1. B. lenta L. Sweet Birch. Black Birch. Cherry Birch. A tree 15-20 m. high, 6-12 dm. in diameter; bark dark-brown,close,. smooth, becoming furrowed, not separating in layers, the young bark having a very sweet wintergreen taste; lenticels prominent; twigs glabrous, slender and pliable, red-brown; fruiting catkins short-cylindric, 1.5-3.5 cm. long, the scales firm and smooth; nut oblong, with narrow wings. Rich woods, Maine to Ontario, south to Georgia and Tennessee (Fig. 53 ).
2. B. lutea Michx, f. Yellow Birch. A tree 20-30 m. high, and 6-12 dm. in diameter; bark of trunk yellowish or silvery-gray, detaching in thin filmy layers; twigs gray-brown, somewhat aromatic; fruiting catkins oblong, 2-4 cm. Jong, the scales pubescent; nut oblong, with narrow wings. Rich cool woods, Nova Scotia to Ontario, south to North Carolina and Iowa (Fig. 54 ).
3. B. nigra L. River Birch. Red Birch. A tree 15-30 m. high, 3-9 dm. in diameter; bark reddish-brown, deeply furrowed and broken into thin irregular scales, exposing the orange-red close bark underneath; twigs reddish; buds hairy, the lower scales elongated; fruiting catkins thick-cylindric, 2. 5-3. 5 cm. long, the scales tomentose; nut broadly ovate, winged, pubescent. Bottomlands, Florida to Texas, north to New Hampshire, Michigan, Minnesota, and Kansas (Fig. 55).
Fig. 53. Befula lenta.
Fig. 54. Betula lutea.
Fig. 55. Betula nigra.
Fig. 56. Betula populifolia.
Fig. 57. Betula papyrifera.
4. B. populifolia Marsh. Gray Birch. Bushy tree up to 20 m. high; bark close, not exfoliating, chalky-white with dark elongate markings; twigs slender, glabrous, wiry, often resinous-warty; buds ovoid, glabrous, about 6 mm. long; fruiting catkins 1.8 cm. long. Sterile soil, Prince Edward Island to Quebec, south to Delaware and Indiana (Fig. 56).
5. B. papyrifera Marsh. Paper Birch. Canoe Birch. A tree up to 25 m. high, with a trunk diameter of 1 m. ;bark lustrous, white or bronze, peeling in thin layers; buds glabrous;fruiting catkins 1. 5-4. 5 cm. long, spreading or drooping on slender peduncles, the scales ciliate-margined. Woods, Labrador to Alaska, south in the Appalachians to West Virginia and North Carolina, in the western mountains to Montana and Washington (Fig. 57),