Trees or shrubs, winter-deciduous, sometimes rhizomatous. Terminal buds absent, pseudoterminal bud (axillary bud of youngest leaf) ovoid, with 2 unequal opposite outer scales enclosing several imbricate inner scales. Leaves: stipules prominent on new growth, soon deciduous. Leaf blade thin, somewhat leathery, secondary veins unbranched, ±parallel, extending to margin, each vein ending in sharp tooth or well-developed awn. Inflorescences staminate or androgynous, axillary, spicate, erect, rigid or flexible; androgynous inflorescences with pistillate cupules/flowers toward base and staminate flowers distally. Staminate flowers: sepals distinct; stamens 12(-18), typically surrounding indurate pistillode covered with silky hairs. Pistillate flowers 1-3 per cupule; sepals distinct; carpels and styles typically 6(-9). Fruits: maturation in 1st year following pollination (termed annual by many authors); cupule 2-4-valved, valves connate marginally until maturity, ±completely enclosing nut(s), spiny, spines irregularly branched, often interlocking, densely or sparsely covered in simple hairs; nuts 1-3 per cupule, plano-convex, or if 3, then central nut often reduced and flattened, or if solitary, then often rounded in cross section, not winged, adjacent nuts not separated by internal cupule valves. x = 12.
North America, Europe, Asia.
Species ca. 8-10 (3 in the flora, often interpreted as 2).
As evidenced by United States breeding programs, all species are probably interfertile (including American × Asian species). Local morphologic intergradation between species is to be expected.
Paillet, F. L. and P. A. Rutter. 1989. Replacement of native oak and hickory tree species by the introduced American chestnut Castanea dentata in southwestern Wisconsin, USA. Canad. J. Bot. 67: 3457-3469.
|1||Cupules 4-valved, enclosing 3 flowers/fruits; leaf blade abaxially without stellate trichomes, appearing glabrous, with minute multicellular glands, these often embedded on blade, and simple trichomes on veins; nut obovate, flattened at least on 1 side, beak thin, flexible, to 8 mm or more excluding styles.||Castanea dentata|
|1||Cupules 2-valved, enclosing 1 flower/fruit; leaf blade abaxially bearing stellate trichomes (occasionally visible only with magnification), often with simple trichomes on veins; nut round in cross section, ovoid-conic, beak less than 3mm excluding styles.||> 2|
|2||Longest spines of cupule often exceeding 10 mm; young twigs glabrous; petiole usually 8–10(–15) mm; bark brownish, moderately to deeply fissured.||Castanea ozarkensis|
|2||Longest spines of cupule usually less than 10 mm; young twigs puberulent (sometimes glabrate with age); petiole usually 3–7(–10) mm; bark gray to brown, smooth, not fissured or only shallowly fissured.||Castanea pumila|