Flower:

Male and female flowers are borne separately on the same tree (monoecious), in clusters called catkins. Male catkins are in groups of 1 to 3 at tips of 1 year old twigs, pendulous in flower, 2 to 3¾ inches long, developing in fall as a slender spike of tightly appressed scales and opening up the following spring.

Female catkins are erect or ascending, cylindrical, ½ to 1 inch long from new, spur-like lateral branches on the same branch as the males. Styles are bright red.

Leaves and stems:

Leaves are alternate and simple in mostly 2s or occasionally 3s on short, spur-like lateral branches, and singly on the new, elongating terminal branches. The blade is broadly egg-shaped, larger towards the base, 2 to 3½ inches long, 1¼ to 2 1/3 inches wide, abruptly tapered to a sharply pointed tip, the base rounded to nearly straight across, on a 1/3 to 1 inch, typically hairless stalk. Edges are irregularly double-toothed, the upper surface dark green and sparsely hairy becoming smooth, the lower surface lighter green with hairs on veins and in vein axils. Leaves have 9 or fewer pairs of lateral veins.

Twigs are brown to reddish brown or even deep maroon, with scattered lenticels (pores), the new growth hairy but quickly becoming mostly hairless, then smooth the second year.

Bark is reddish brown on young branches becoming chalky white on larger branches and the upper trunk, peeling in papery horizontal strips. Older bark on the lower trunk turns dark gray, furrowed and scaly. Trunks can reach 20 inches diameter at breast height (dbh), though more commonly 12 to 16 inches. Trunks are often single but clusters of multiple trunks are not uncommon.

Fruit:

Female catkins become pendulous or nearly so, cylindric, cone-like clusters, ¾ to 1¾ inch long.

Fruit is a winged nutlet 1/8 to ¼ inch long, subtended by the persistent, hairy, 3-lobed scale. Fruits are released throughout fall and winter, littering the snow around a tree with seeds and scales.

Notes:

To simply say Birch, for most people means Paper Birch. White forests of the northern lakes and woods, birch bark canoes, fine cabinetry lumber, hot and aromatic woodfires, even fine birch beer for those who have ventured there. Its mature bark is white, not yellow, gray or pink. Though most similar to Heart-leaved Birch (Betula cordifolia), its leaves are just that—the bases are heart-shaped, rarely rounded, and 9 to 12 pairs of lateral veins where Paper Birch leaves have 9 or fewer vein pairs and bases are rounded to nearly straight across. For all its beauty, too many find out the hard way Paper Birch is not adapted to urban landscapes or any extensive mucking around with a closed forest canopy and brushy understory in which they grow naturally. Birch is best adapted to cooler, even moisture conditions that a forest ecology provides. While birch can grow just fine in hotter drier locations, these conditions invariably weaken its ability to fight off the bronze birch borer, a native and ubiqutous insect that is almost always fatal to susceptible, affected trees.