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1 Fruits globose and pointed at apex; external surface of nuts smooth; [cultivated as an ornamental, rarely escaped or persistent]; [section Cardiocaryon]
1 Fruits either globose and rounded at apex, or ellipsoid and acute at apex; external surface of nuts complexly ridged; [native, collectively widespread]; [section Rhysocaryon].
..2 Fruits 1.4-3.5 cm wide (in diameter); nuts 1.1-1.7 cm long; [OK and TX westwards and southwestwards].
....3 Fruits 2.0-3.5 cm wide (in diameter); nuts 1.8-2.7 cm long; leaflets 9-15 per leaf
..2 Fruits 3.5-8.0 cm wide (in diameter); nuts 3.0-6.0 cm long; [collectively widespread in our area].
......4 Lower surface of the leaflets densely hirsute with 4-8-rayed fascicled hairs; fruits ellipsoid, densely pubescent with reddish-brown glandular hairs; leaf scars with a velvety ridge along the upper margin; leaves with (7-) 11-17 leaflets; pith dark brown; terminal buds 12-18 mm long; bark of mature trees pale.
......4 Lower surface of the leaflets hirsute with single and 2-rayed fascicled hairs; fruits spherical or nearly so, lepidote with peltate scales and occasional glandular hairs; leaf scars without a velvety ridge along the upper margin; leaves with (9-) 15-19 (-23) leaflets; pith light brown; terminal buds 8-10 mm long; bark of mature trees dark