The following is taken from Robert E. Swanson's A Field Guide to the Trees and Shrubs of Southern Appalachians:
1 Leaves thick and leathery, evergreen:
2 Leaves abundantly dotted beneath with small, yellowish to brownish scales or pits (visible under hand lens)..............................................................R. minus
2' Leaves not dotted beneath with small scales or pits:
3 Leaves 12-30 cm long, wedge shaped at base; flower bud with long, thin leafy bracts.................................................R. maximum
3' Leaves 8-15 cm long, rounded at base; flower buds without leafy bracts............................................................R. catawbiense
1' Leaves not thick and leathery, deciduous:
4 Upper surface of leaves bright green or dull green, not lustrous:
5 Leaves densely grayish-hairy beneath, at least along midrib and larger veins, with a mixture of long coarse hairs and short curly hairs..................................................................R. calendulaceum
5' Leaves nearly glabrous beneath or merely with coarse or still appressed hairs on lower midrib:
6 Leaves narrowly to broadly elliptical; apex of leaves gradually tapering to along point....R. vaseyi
6' Leaves, or some of them, obovate; apex of leaves tapering to a short point or somewhat blunt...............................................R. nudiflorum
4' Upper surface of leaves dark green and lustrous:
7 Young twigs and lower surface of leaves essentially glabrous.................................................................R. aborescens
7' Young twigs more or less bristly, at least neat tip, with coarse brown hairs; lower surface of leaves with long stiff hairs on midrib.......................................................................R. viscosum
[1] Swanson, R.E. 1994. A Field Guide to the Trees and Shrubs of the Southern Appalachians. John Hopkins University Press, Baltimore.
