River birch (Betula nigra)
Height 40' to 60' with a diameter of up to 24"; a mature tree usually has a short trunk that divides into several large ascending limbs that compose an open, irregular crown of slender drooping branchlets.
Dark brown at base of old trunks, deeply furrowed; higher up on main stem and on larger branches, becomes lustrous reddish brown; peels more or less freely; twigs, reddish color with white dots (lenticels).
Simple, alternate on stem, length 1-1/2" to 3"; more or less triangular with double-toothed edges; upper surface dark green, lower surface pale yellow green; turns yellow in autumn.
Winged nutlets densely crowded into a cone-shaped catkin about 1" long; ripens in late spring or early summer.
Grows along rich bottom lands of streams and rivers in the southeastern corner of the state, especially in the Mississippi and Root River valleys; common along Mississippi River as far as Wabasha County; also reported near Mankato; shade intolerant, moderately fast growing.