Trees, with smooth gray bark becoming on old trunks rough or scaly, strong hard tough brown heartwood, pale sapwood and tough terete flexible branchlets, solid pith, buds covered with few valvate or with numerous imbricated scales, the axillary buds much smaller than the terminal. Leaves often glandular-dotted, their petioles sometimes persistent on the branches during the winter, and in falling leaving large elevated oblong or semiorbicular more or less 3-lobed emarginate leaf-scars displaying small marginal clusters and central radiating lines of dark fibro-vascular bundle-scars; leaflets involute in the bud, ovate or obovate, usually acuminate, thick and firm, serrate, mostly unequal at base, with veins forked and running to the margins; turning clear bright yellow in the autumn. Aments of the staminate flowers ternate, slender, solitary or fascicled in the axils of leaves of the previous or rarely of the current year, or at the base of branches of the year from the inner scales of the terminal bud, the lateral branches in the axils of lanceolate acute persistent bracts; calyx usually 2 rarely 3-lobed, its bract free nearly to the base and usually much longer than the ovate rounded or acuminate calyx-lobes; stamens 3—10, in 2 or 3 series, their anthers ovate-oblong, emarginate or divided at apex, yellow or red, pilose or hirsute, as long or longer than their slender connectives; pistillate flowers sessile, in 2—10-flowered spikes, with a perianth-like involucre, slightly 4-ridged, unequally 4-lobed at apex, villose and covered on the outer surface with yellow scales more or less persistent on the fruit, the bract much longer than the bractlets and the single calyx-lobe; stigmas short, papillose-stigmatic. Fruit ovoid, globose or pyriform, with a thin or thick husk becoming hard and woody at maturity, 4-valved, the sutures alternate with those of the nut, sometimes more or less broadly winged, splitting to the base or to the middle; nut oblong, obovoid or subglobose, acute, acuminate, or rounded at apex, tipped by the hardened remnants of the style, narrowed and usually rounded at base, cylindric, or compressed contrary to the valves, the shell thin and brittle or thick, hard, and bony, smooth or variously rugose or ridged on the outer surface, 4-celled at base, 2-celled at apex. Seed compressed, variously grooved on the back of the flat or concave lobes, sweet or bitter. _Carya_ is confined to the temperate region of eastern North America from the valley of the St. Lawrence River to the highlands of Mexico, and to southern China where one species occurs. Of the seventeen species, fifteen inhabit the territory of the United States. The generic name is from Καρύα, an ancient name of the Walnut. CONSPECTUS OF THE SPECIES OF THE UNITED STATES.