Hickory

Hickory is a common name for trees composing the genus Carya, which includes 19 species accepted by Plants of the World Online.

Seven species are native to southeast Asia in China, Indochina, and northeastern India (Assam), and twelve are native to North America. A number of hickory species are used for their edible nuts or for their wood.

The name "hickory" derives from a Native American word in an Algonquian language (perhaps Powhatan). It is a shortening of pockerchicory, pocohicora, or a similar word, which may be the name for the hickory tree's nut, or may be a milky drink made from such nuts. The genus name Carya is Ancient Greek: κάρυον, káryon, meaning "nut".

Hickories are temperate to subtropical forest trees with pinnately compound leaves and large nuts. Most are deciduous, but one species (C. sinensis, syn. Annamocarya sinensis) in southeast Asia is evergreen.

Hickory flowers are small, yellow-green catkins produced in spring. They are wind-pollinated and self-incompatible. The fruit is a globose or oval nut, 2–5 cm (1–2 in) long and 1.5–3 cm (1⁄2–1+1⁄4 in) diameter, enclosed in a four-valved husk, which splits open at maturity. The nut shell is thick and bony in most species, but thin in a few, notably the pecan (C. illinoinensis); it is divided into two halves, which split apart when the seed germinates.

Some fruit are borderline and difficult to categorize. Hickory (Carya) nuts and walnut (Juglans) nuts, both in the family Juglandaceae, grow within an outer husk; these fruit are sometimes considered to be drupes or drupaceous nuts, rather than true botanical nuts. "Tryma" is a specialized term for such nut-like drupes. The Angiosperm Phylogeny Group, however, considers the fruit to be a nut.

The oldest fossils attributed to Carya are Cretaceous pollen grains from Mexico and New Mexico. Fossil and molecular data suggest the genus Carya may have diversified during the Miocene. Modern Carya first appear in Oligocene strata 34 million years ago. Recent discoveries of Carya fruit fossils further support the hypothesis that the genus has long been a member of Eastern North American landscapes, however its range has contracted and Carya is no longer extant west of the Rocky Mountains.

Fossils of early hickory nuts show simpler, thinner shells than modern species with the exception of pecans, suggesting that the trees gradually developed defenses to rodent seed predation.^{[citation needed]} During this time, the genus had a distribution across the Northern Hemisphere, but the Pleistocene Ice Age beginning 2 million years ago obliterated it from Europe. In Anatolia, the genus appears to have disappeared only in the early Holocene, probably related to human disturbance. The distribution of Carya in North America also contracted and it completely disappeared from the continent west of the Rocky Mountains. It is likely that the genus originated in North America, and later spread to Europe and Asia.