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, 1½ to 3½ inches long, developing in fall as a slender spike of tightly appressed scales and opening up the following spring. Female catkins are erect and stout, cylindrical, 1/3 to ½ inch long from new, spur-like lateral twigs on the same branch as the males.

Leaves and bark:

Leaves are alternate and simple in 2s or 3s on short, spur-like lateral twigs, and singly on the new, elongating terminal branchlets. The blade is broadly lance-shaped to nearly diamond-shaped, widest towards the base, 2 to 4 inches long, 1¼ to 2¾ inches wide, pointed at the tip, wedge-shaped to obscurely angled at the base, on a ¼ to 1/3 inch hairy stalk. Edges are coarsely and deeply 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.

Twigs are brown to reddish brown with scattered lenticels (pores), new growth is hairy becoming mostly hairless and shiny the second year.

Bark is light reddish brown to salmon pink to creamy colored, typically very papery-shaggy and peeling in layers on younger stems and branches, older bark becoming coarse with gray, scaly plates on the lower trunk. Trunks can reach 20 inches diameter at breast height (dbh), though more commonly 12 to 16 inches.

Fruit:

Female catkins become erect to ascending, oval to cylindric, cone-like clusters, ¾ to 1¼ inch long, of winged nutlets each 1/8 to ¼ inch long, green drying to brown.

Notes:

Naturally occurring only in the floodplain forest of the Mississippi River in southestern Minnesota, River Birch might not be so familiar to people if it wasn't used so extensively in urban landscape plantings. While our other four native birch species are restricted to the cooler northern temperate zone, River Birch's North American range extends all the way south the the Gulf of Mexico. This higher heat tolerance is one reason River Birch is not so susceptible to the bronze birch borer that is so lethal to our other species when planted in hotter and drier urban sites. The deeply salmon pink, often heavily exfoliating bark and deeply double toothed leaves with wedge-shaped bases easily distinguish this from other birches.