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 Leaves elliptic to oblanceolate, mostly < 15 cm long, the apices acute to obtuse; twigs puberulent; spine-covered husk of fruit splitting into 2 sections, enclosing 1 nut; nut circular in cross-section, 7-19 mm in diameter; pistillate dichasia of 1 flower; leaves with stellate trichomes, with few bulbous-based trichomes when young, puberulent, pilose, tomentulose, or tomentose in age (usually rather densely so).
..2 Longest spines of the fruit husk usually > 10 mm long; young twigs glabrous; petiole 8-10 (-15) mm long; [plants of AR, OK, MO, and n. LA]
1 Leaves elliptic, oblanceolate or lanceolate, 8-30 cm long, the apices acuminate, sometimes only shortly so; spine-covered husk of fruit splitting into 4 sections, enclosing 1-3 (-5) nuts; nut flattened on at least one side, 18-30 mm in diameter; pistillate dichasia of 3 flowers; leaves with or without stellate trichomes; twigs puberulent or glabrous.
....3 Undersurface of leaves densely covered with bulbous-based trichomes when young, essentially glabrous in age; leaves mostly > 15 cm long, generally long-acuminate; twigs glabrous; trees single-trunked; spines of fruit husk weak, easily bent
......4 Leaf margins ciliate; young twigs glaucous; burs with 1 nut
....3 Undersurface of leaves persistently and densely tomentose beneath; leaves mostly < 15 cm long, generally short-acuminate; twigs puberulent; trees multi-trunked from base; spines of fruit husk stiff.
........5 Leaf undersurface covered with yellowish brown to yellowish gray scalelike glands (as well as tomentose)