Click the number at the start of a key lead to highlight both that lead and its corresponding lead. Click again to show only the two highlighted leads. Click a third time to return to the full key with the selected leads still highlighted.
1 Shrub to 4 m tall; leaf blades crenate to blunt-dentate; [n. NJ and c. OH northwards]; [subgenus Betula]
....3 Leaves broadly cuneate at the base; inner bark of the twigs bitter, not aromatic; [subgenus Betulaster]
......4 Bark of stems 5-30 cm in diameter (on larger trees look up for branches) yellow or yellowish-gray, exfoliating in papery shreds (bark of larger trunks becoming platey, the plates not prominently marked horizontally by old lenticels); scales of fruiting catkins 6-13 mm long, pubescent across the surface and also marginally ciliate; twigs and buds slightly hairy; leaf teeth usually < 6 per cm of midleaf margin; leaves persistently hairy beneath
......4 Bark of stems 5-30 cm in diameter (on larger trees look up for branches) reddish-brown or dark brown, tight (bark of larger trunks becoming platey, the plates prominently marked horizontally by old lenticels); scales of fruiting catkins 5-7 mm long, glabrous across the surface (though ciliate-margined; twigs and buds glabrous; leaf teeth usually ≥ 6 per cm of midleaf margin; leaves glabrous soon after unfurling.
........5 Leaf blades mostly 2-6 cm long, suborbicular, the apex rounded; secondary veins 3-6 per leaf side; [of Smyth County in sw. VA]
........5 Leaf blades ovate or triangular, 7-15 cm long, the apex acute to acuminate; secondary veins 9-12 per leaf side; [widespread in the Mountains, and northward also the Piedmont and Coastal Plain of our area]
............ 7 Leaf apex long-acuminate, but not attenuate; infructescence scales sparsely pubescent on the outer surface; bark of mature trees creamy to bright white
............ 7 Leaf apex attenuate-acuminate; infructescence scales densely pubescent on the outer surface; bark of mature trees grayish white
............ ..8 Leaf blades 3-4 (-6) cm long, with 3-6 lateral veins on each side of the midvein
............ ....9 Leaf blades cordate (rarely rounded) at the base, with (8-) 9-12 pairs of lateral veins; scales of carpellate aments 5.6-8.7 mm long, the lateral lobes upturned (curved towards the apex); bark of mature trees pink-white to brown-white or red-brown-white; twigs glabrous or slightly pubescent (and then glabrate in age); lenticels of young twigs large, the smallest ca. 1 mm; leaf margins singly serrate to obscurely doubly-serrate
............ ....9 Leaf blades broadly cuneate to truncate at the base, with 6-9 pairs of lateral veins; scales of carpellate aments 3.9-6.2 mm long, the lateral lobes divergent (curved outwards, away from the apex); bark of mature trees chalky white (rarely light brown to dark brown); twigs densely pubescent; lenticels of young twigs variable in size, the smallest about 0.25 mm; leaf margins usually obviously doubly-serrate