1. Leaves entire to deeply lobed, or (3 species) if coarsely serrate, then finely stellate-pubescent over the lower surface; nut an “acorn,” terete, seated (solitary) in a shallow to deep scaly cup which remains intact.
1. Leaves sharply and regularly serrate, glabrous to silky-pubescent (not stellate) along the veins beneath; nut slightly to strongly flattened on at least one side, enclosed (usually 2–3 together) in a prickly involucre (husk or bur), which splits into (2–) 4 valves.
2. Teeth of leaves mostly 2–5 mm long, acuminate and often somewhat incurved; flowers in midsummer, after leaves are fully developed, the staminate ones in elongate, stiff, essentially sessile aments; fruiting involucre over 2 cm long, densely covered with stiff and sharp branched spines and normally containing 2–3 somewhat flattened but not sharply angled nuts; winter buds less than 1 cm long; bark ridged and furrowed, brownish.
2. Teeth of leaves at most 1.5 (–2) mm long (measured along upper margin); flowers appearing in spring, at same time as the leaves, the staminate ones in a peduncled, pendent, spherical ament; fruiting involucre ca. 2 cm long or less, bearing weak unbranched spines and normally containing 2 sharply 3-angled nuts; winter buds over 1 cm long; bark smooth and gray.