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..
A shrub or small tree, the close bark dark reddish-brown, the young twigs finely pubescent. Leaves oval to rhombic-ovate, acute at both ends, serrate, 1'-2 1/2 long, firm in texture, dull green above, paler and sparingly pubescent beneath, the slender petioles about 1/2' long; staminate aments 2'-2 1/2' long; fruiting pistillate aments about 1' long, cylindric, slender-stalked; bracts about 2" long and broad, pubescent, the middle lobe obtuse or acute, longer than the obtuse lateral ones; nut narrower than its wings.
Swamps, Minnesota to Saskatchewan and Montana. Spring.
Betula pumila L. Mant. 124. 1767.
A bog shrub, 2°-15° tall, the twigs brown, becoming glabrous, the young foliage densely brown ish-tomentose. Leaves obovate, broadly oval or orbicular, rounded at both ends or some of them cuneate-narrowed at the base, rather coarsely dentate, when mature glabrous and dull green above, pale, persistently tomentose or becoming glabrous beneath and prominently reticulate-veined, 1/2'-1 1/2' long; petioles 1 1/2'-3" long; fruiting pistillate aments oblong-cylindric, erect, peduncled, 1' long or less, about 3" in diameter; bracts puberulent or ciliolate, the lateral lobes spreading at right angles, shorter than the middle one; nut oblong, mostly rather broader than its wings.
In bogs, Newfoundland to western Ontario and the Northwest Territory, south to New Jersey, Ohio and Minnesota. Also in Europe and Asia. Dwarf birch. Tag-alder. May-June.
Betula glandulifera (Regel) Butler, differs in having leaves smooth or nearly so on both sides. It grows from Michigan and western Ontario to British Columbia.
Betula nana L. Sp. PI. 983. 1753. B. Michauxii Spach, Ann. Sci. Nat. (II.) 15: 195. 1841.
A low diffuse shrub, similar to the preceding species, but the twigs glandless, puberulent or glabrous. Leaves orbicular, obovate, or reniform and wider than long, bright green, firm, glabrous, on both sides when mature, deeply and incisely crenulate, rounded at the apex, rounded, obtuse or cuneate at the base, 3"-10" long; petioles rarely more than 1" long; staminate aments 1/2'-1' long, solitary or clustered; pistillate aments oblong, sessile or short-peduncled, erect or somewhat spreading, 3"-5" long; fruiting bracts glabrous, the lower usually 3-lobed, the upper ovate or lanceolate, mostly entire; nut oblong, wingless or narrowly winged.
Greenland and Labrador to Hudson Bay. Also in northern Europe and Asia. May-June.