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.
Etymology The name "hickory" derives from clipping of the native Algonquian (perhaps Powhatan) word pockerchicory, pocohicora, or something else similar 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".
Description 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 fruits are borderline and difficult to categorize. Hickory (Carya) nuts and walnut (Juglans) nuts, both in the family Juglandaceae, grow within an outer husk; these fruits 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.
Taxonomy
Phylogeny 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 appeared 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. 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.
Subdivision The genus Carya (not to be confused with Careya in the Lecythidaceae) is in the walnut family, Juglandaceae. In the APG system, this family is included in the order Fagales. Several species are known to hybridize, with around nine accepted, named hybrids.
Asian hickories Carya sect. Sinocarya
Carya dabieshanensis M.C. Liu – Dabie Shan hickory (may be synonymous with C. cathayensis) Carya cathayensis Sarg. – Chinese hickory Carya hunanensis W.C.Cheng & R.H.Chang – Hunan hickory Carya kweichowensis Kuang & A.M.Lu – Guizhou hickory Carya luana C.Y.Deng & X.G.Xiang Carya luodianensis Yang, Y. B (2026) Carya poilanei Leroy – Poilane's hickory Carya sinensis Dode – Beaked hickory Carya tonkinensis Lecomte – Vietnamese hickory C. sinensis has sometimes been split out in a separate genus as Annamocarya sinensis, but not by Plants of the World Online, as genetic data support it being embedded within the other Asian Carya.
North American hickories Carya sect. Carya – typical hickories
Carya floridana Sarg. – scrub hickory Carya glabra (Mill.) Sweet – pignut hickory, pignut, sweet pignut, coast pignut hickory, smoothbark hickory, swamp hickory, broom hickory Carya laciniosa (Mill.) K.Koch – shellbark hickory, shagbark hickory, bigleaf shagbark hickory, kingnut, big shellbark, bottom shellbark, thick shellbark, western shellbark Carya myristiciformis (F.Michx.) Nutt. – nutmeg hickory, swamp hickory, bitter water hickory Carya ovalis (Wangenh.) Sarg. – red hickory, spicebark hickory, sweet pignut hickory (treated as a variety of C. glabra by Flora N. Amer. and Plants of the World Online) Carya ovata (Mill.) K.Koch – shagbark hickory C. o. var. ovata – northern shagbark hickory C. o. var. australis – southern shagbark hickory, Carolina hickory (syn. C. carolinae-septentrionalis) Carya pallida (Ashe) Engl. & Graebn. – sand hickory Carya texana Buckley – black hickory Carya tomentosa (Poir.) Nutt. – mockernut hickory (syn. C. alba) †Carya washingtonensis Manchester – Miocene of Kittitas County, Washington
Carya sect. Apocarya – pecans
Carya aquatica (F.Michx.) Nutt. – bitter pecan or water hickory Carya cordiformis (Wangenh.) K.Koch – bitternut hickory Carya illinoinensis (Wangenh.) K.Koch – pecan Carya palmeri W.E. Manning – Mexican hickory
Distribution and habitat Seven species are native to southeast Asia in China, Indochina, and northeastern India (Assam), and twelve are native to North America, of which eleven occur in the United States, four in Mexico (of which one, C. palmeri, endemic there), and five extending into southern Canada.
Ecology Hickory is used as a food plant by the larvae of some Lepidoptera species. These include:
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