Trees or rarely shrubs, monoecious, evergreen or deciduous. Stipules usually early deciduous. Leaves alternate, sometimes false-whorled in Cyclobalanopsis. Inflorescences unisexual or androgynous with female cupules at the base of an otherwise male inflorescence. Male inflorescences a pendulous head or erect or pendulous catkin, sometimes branched; flowers in dense cymules. Male flower: sepals 4-6(-9), scalelike, connate or distinct; petals absent; filaments filiform; anthers dorsifixed or versatile, opening by longitudinal slits; with or without a rudimentary pistil. Female inflorescences of 1-7 or more flowers subtended individually or collectively by a cupule formed from numerous fused bracts, arranged individually or in small groups along an axis or at base of an androgynous inflorescence or on a separate axis. Female flower: perianth 1-7 or more; pistil 1; ovary inferior, 3-6(-9)-loculed; style and carpels as many as locules; placentation axile; ovules 2 per locule. Fruit a nut. Seed usually solitary by abortion (but may be more than 1 in Castanea, Castanopsis, Fagus, and Formanodendron), without endosperm; embryo large.
Trees or shrubs , evergreen or deciduous, shrubs sometimes rhizomatous. Winter buds sessile, with few to many imbricate scales (2 valvate scales enclosing imbricate scales in Castanea ); terminal bud present or absent. Leaves alternate, spirally arranged, simple; stipules deciduous (usually), distinct, scarious; petiole present. Leaf blade lobed or unlobed, pinnately veined, margins serrate, dentate, or entire; surfaces usually pubescent, at least when young, sometimes with scales. Inflorescences unisexual or androgynous catkins; staminate and androgynous catkins spicate or capitate, rigid, flexible, or lax, consisting of few- to many-flowered clusters, bracts present or absent; pistillate catkins rigid or flexible, with 1-several spicately arranged, rarely solitary, terminal cupules bearing 1-3(-15 or more) pistillate flowers. Staminate flowers bracteate, bracts often caducous; sepals (3-)4-6(-8); stamens (3-)6-12(-18 or more); petals absent; anthers 2-locular, dehiscing by longitudinal slits, pollen sacs contiguous; pistillode often present and indurate, or vestigial as central tuft of trichomes. Pistillate flowers: calyx of 4-6 distinct or connate sepals; petals absent; pistil 1, 3(-6 or more)-carpellate; ovary inferior, locules as many as carpels; placentation axile; ovules pendulous, 2 in each locule, all but 1 in each pistil usually aborting; styles as many as carpels, distinct to base; stigmas dry; staminodes present or absent. Fruits nuts, sometimes winged, 1-seeded, subtended or enclosed individually or in groups of 2-3(-15) by scaly or spiny, multibracteate cupule; seed coat membranous; endosperm none; embryo straight, as long as seed; cotyledons fleshy, starchy or oily.
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