5. Carpinus. Each nut subtended by an enlarged leafy bractlet.
Tribe III. QUERCINEÆ. Sterile flowers with 4–7-lobed calyx and stamens indefinite (3–20). Fertile flowers 1 or few, enclosed in a cupule consisting of consolidated bracts, which becomes indurated (scaly or prickly) and surrounds or encloses the nut.
[*] Sterile flowers in slender catkins.
6. Quercus. Cupule 1-flowered, scaly and entire; nut hard and terete.
7. Castanea. Cupule 2–4-flowered, forming a prickly hard bur, 2–4-valved when ripe.
[*][*] Sterile flowers in a small head.
8. Fagus. Cupule 2-flowered, 4-valved, containing 2 sharply triangular nuts.
Sterile flowers 3, and bractlets 2, to each shield-shaped scale or bract of the catkins, consisting each of a calyx of one scale bearing 4 short filaments with 1-celled anthers (or strictly of two 2-parted filaments, each division bearing an anther-cell). Fertile flowers 2 or 3 to each 3-lobed bract, without bractlets or calyx, each of a naked ovary, becoming a broadly winged and scale-like nutlet (or small samara) crowned with the two spreading stigmas.—Outer bark usually separable in sheets, that of the branchlets dotted. Twigs and leaves often spicy-aromatic. Foliage mostly thin and light. Buds sessile, scaly. Sterile catkins long and drooping, terminal and lateral, sessile, formed in summer, remaining naked through the succeeding winter, and expanding their golden flowers in early spring, with or preceding the leaves; fertile catkins oblong or cylindrical, peduncled, usually terminating very short 2-leaved early lateral branches of the season. (The ancient Latin name, of Celtic origin.)
[*] Trees, with brown or yellow-gray bark, sweet-aromatic as well as the twigs, membranaceous and straight-veined Hornbeam-like leaves heart-shaped or rounded at base, on short petioles, and sessile very thick fruiting catkins; their scales about equally 3-cleft, rather persistent; wing of fruit not broader than the seed-bearing body.