B. alba: tree; leaves deciduous, ovate-deltoid, varying to broadly cordate, and with a rhomboidal tendency, acute, unequally serrated, glabrous, often with resinous spots; male catkins cylindrical, drooping, 1-2 inches long, females shorter and more compact. - Woods. Fl. March, April.
The Common Birch, B. glutinosa, and the White Birch, B. alba, are two slightly different forms: the first having the fruits broadly obovate, and the lateral lobes of the 3-lobed scales of the female catkins ascending; the second having the fruits obovate-elliptical, and the lobes falcate reflexed.
B. nana: shrub; leaves deciduous, small, nearly orbicular, crenate, not pointed; catkins small, oblong, erect. - Spongy Bogs. Fl. May.