This section is from the book "An Illustrated Flora Of The Northern United States, Canada And The British Possessions Vol1", by Nathaniel Lord Britton, Addison Brown. Also available from Amazon: An Illustrated Flora of the Northern United States, Canada and the British Possessions. 3 Volume Set..
Betula lutea Michx. f. Arb. Am. 2: 152. pl. 5. 1812.
A large forest tree, reaching a maximum height of about 100° and a trunk diameter of 40, the bark yellowish or gray, separating in thin layers or close, the twigs gray-brown. Leaves ovate or oblong-ovate, mostly acuminate at the apex, rounded, obtuse or rarely sub-cordate at the base, sharply serrulate all around, dark green and dull above, pubescent on the veins beneath, 1 1/2-4' long, petioles 4"9' long; staminate aments usually 2-4 together; pistillate aments sessile, oblong or oblong-cylindric, 1 1/2 or less long, 7"-9' thick in fruit, rather loose; bracts nearly equally 3-lobed to somewhat above the middle, ciliolate, the lateral lobes ascending; nut broadly oblong, wider than its wings.
B. fontinalis Sargent, Bot. Gaz. 31: 239. 1901.
A shrub or rarely a tree attaining a height of about 400 and a trunk diameter of 1 1/2°, the bark smooth, dark bronze, the twigs gray-brown, warty. Leaves broadly ovate or nearly orbicular, acute or obtuse at the apex, sharply serrate, rounded or obtuse at the base, short-petioled, glabrous on both sides or sparingly pubescent on the veins beneath, 1'-2' long; petioles slender, 2"-6" long; pistillate aments peduncled, cylindric, spreading or pendent, l'-l 1/4' long, about 5" in diameter in fruit; fruiting bracts ciliolate, about 3" long, their lateral lobes ascending; nut much narrower than its wings.
South Dakota to western Nebraska, British Columbia, California and New Mexico, and on Mt. Albert, Quebec. Has been confused with Betula occidentalis Hook., and referred to the Asiatic B. microphylla Bunge. Black, gray, sweet or water-birch. April-May.
Betula glandulosa Michx. Fl. Bor. Am. 2: 180. 1803.
A shrub, 1o-6o high, the twigs brown, glandular-warty, not pubescent. Leaves orbicular, reniform, oval or obovate, glabrous, rounded at the apex, rounded, narrowed or cuneate at the base, crenate-dentate, bright green above, pale green and glandular-dotted beneath, short-petioled, 1/4'-1' long; petioles 1"-3" long; staminate aments commonly solitary; about ¥ long; pistillate aments cylindric, erect, peduncled, 5"-12" long and about 2" in diameter in fruit; fruiting bracts 2"-3" long, the lateral lobes rather shorter than the middle one; nut oblong to nearly orbicular, its wings mostly narrow.
Newfoundland to Alaska, the higher mountains of Maine and northern New York, Michigan, Minnesota, in the Rocky Mountains to Colorado, and to California. Also in Asia. Dwarf birch. June-July.