1. Carya Nutt. (hickory)

Twigs with the pith solid and homogeneous in texture. Leaflets (3–)5–13 per leaf, the largest leaflets often near the leaf tip, less commonly uniform in size or the median leaflets slightly larger than the others. Staminate catkins in clusters, sessile or stalked; each flower with 3–10(–15) stamens. Fruits with the husk splitting longitudinally for at least half of the fruit length, releasing the nut. Nuts often with 4 longitudinal ridges, the surface otherwise smooth or shallowly wrinkled. About 17 species, eastern U.S., Canada, Mexico, Asia.

Hickory nuts are composed of a large seed surrounded by several layers of tissue. The fleshy to leathery or somewhat woody husk of the hickory nut develops from the fused bractlets associated with each flower that become enlarged and thickened as the fruit matures. The husk splits and separates from the fruit. The fruit wall is hard (bony) and is known as the shell of the nut; it remains indehiscent and fused to the seed.

Species of Carya fall into two well-defined groups: the pecans (section Apocarya C. DC., including species 1, 2, and 4 below),with bud scales not overlapping, more numerous leaflets, and seeds that are often bitter; and the hickories (section Carya, including species 3 and 5–9) with strongly overlapping bud scales, fewer leaflets, and seeds that are always sweet-tasting.

The true hickories, not the pecans, were the staple plant food of many Missouri cultures for thousands of years (from about 6500 B.C. to 500 A.D.). The seeds are oily, and are rich sources of lipids, fiber, and starch. The protein content is moderate, and the amino-acid content of the protein is well balanced for human consumption. Unlike some other nuts, hickories do not need to be cooked or leached before eating. Hickories set seed in the fall; they are easy to gather and store, and are abundant in most years. Once the nut is free from the husk, it is impossible to remove it intact from the hard inner shell. Native Americans apparently smashed the nut, removed the large fragments of shell, and ground the nutmeat into a paste, so that smaller fragments of shell were finely ground and not troublesome. Contemporary Americans, with their preference for intact nuts, almost never eat hickories, and only the pecan, Carya illinoinensis, is much used now for human food.

Hickory nuts remain very important as an abundant and nutritious wildlife food. The wood of Carya spp. is strong and stands up well to impact and other shocks. It is widely used for tool handles, ladder rungs, baseball bats, agricultural implements, and other uses requiring shock resistance. It is also widely used for smoking meats.

Hickories are important street trees throughout the state. Their attractive form and often striking golden yellow fall color make them very desirable as street and park trees, but like oaks, the seedling forms a long taproot that makes transplantation difficult. Thus, although several of the species are available commercially, hickories are underutilized in the nursery trade.