Hickory

Lore & Background

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'. Hickories are temperate to subtropical forest trees with pinnately compound leaves and large nuts. Most are deciduous, but one species (C. 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 enclosed in a four-valved husk. The nut shell is thick and bony in most species, but thin in a few, notably the pecan.

Reader's Guide

Hickory trees have been significant for both their edible nuts and their wood. The nuts of some species are palatable, while others are bitter and only suitable for animal feed. Hickory nuts were a significant food source for indigenous peoples of the Eastern Woodlands of North America since the middle Archaic period. Pecans are the most important nut tree native to North America. Hickory wood is hard, stiff, dense and shock resistant, used in tool handles, bows, wheel spokes, walking sticks, drumsticks, and wood flooring. Baseball bats were formerly made of hickory, but are now more commonly made of ash; however, it is replacing ash as the wood of choice. An extract from shagbark hickory bark is used in an edible syrup similar to maple syrup. The Cherokee people would produce a green dye from hickory bark. The ashes of burnt hickory wood were traditionally used to produce a strong lye fit for soapmaking. Ecologically, hickory is used as a food plant by the larvae of several Lepidoptera species, including the luna moth and regal moth.

Did You Know?

• The oldest fossils attributed to Carya are Cretaceous pollen grains from Mexico and New Mexico.
• Modern Carya first appeared in Oligocene strata 34 million years ago.
• The Pleistocene Ice Age obliterated the genus from Europe.
• Hickory nuts are sometimes considered drupes or drupaceous nuts, with 'tryma' a specialized term for such nut-like drupes.

Deep Roots — Evolutionary History and Range Contraction

The story of hickory stretches back millions of years. The oldest physical evidence attributed to the genus Carya consists of Cretaceous-era pollen grains recovered from sites in Mexico and New Mexico. Molecular and fossil data together point to a period of diversification during the Miocene, while the first clearly modern Carya specimens appear in Oligocene strata dating to roughly thirty-four million years ago. Fruit fossils reinforce the idea that hickory has been a fixture of Eastern North American forests for a very long time.

Early hickory nuts, preserved in the fossil record, bore noticeably simpler and thinner shells than those of most living species, with the pecan as a notable exception. This pattern suggests the trees gradually evolved tougher armor as a defense against rodent seed predation. At one point the genus enjoyed a broad Northern Hemisphere distribution. The Pleistocene Ice Age, which began around two million years ago, wiped hickory out of Europe entirely. In Anatolia, the last holdouts vanished only in the early Holocene, likely due to human activity. In North America, the range shrank until the genus disappeared completely from lands west of the Rocky Mountains. Evidence favors North America as the original homeland, with later dispersal into Europe and Asia.

A Genus of Nineteen — Taxonomy and Geographic Spread

Plants of the World Online currently recognizes nineteen hickory species within the genus Carya. Seven of these are native to Southeast Asia, found across China, Indochina, and the northeastern Indian state of Assam. The remaining twelve are North American, with eleven occurring in the United States, four in Mexico (one of which, Carya palmeri, is endemic to that country), and five extending into southern Canada.

Taxonomically, Carya sits within the walnut family Juglandaceae, which the APG system places in the order Fagales. The genus is divided into three sections: Sinocarya for the Asian species, Carya for the typical hickories of North America, and Apocarya for the pecan group. Several species are known to cross-pollinate, producing around nine accepted, named hybrids. One Asian species, Carya sinensis, has occasionally been proposed for its own genus as Annamocarya, but genetic data support keeping it embedded within the broader Carya clade rather than separating it out.

Architecture of a Nut — Morphology and the Botanical Debate

Hickory trees grow in temperate to subtropical forests, bearing pinnately compound leaves and producing large nuts. Most species are deciduous, though one Southeast Asian member, Carya sinensis, retains its foliage year-round. In spring, the trees produce small, yellow-green catkins that are wind-pollinated and self-incompatible, meaning a single tree cannot fertilize itself.

The resulting fruit takes the form of a round or oval nut, roughly two to five centimeters long and one and a half to three centimeters wide, wrapped in a husk with four valves that split apart once the nut matures. In most species the shell is dense and hard, though in the pecan it remains comparatively thin. Each nut splits into two halves that separate at the moment of germination.

Botanists have long debated the precise classification of hickory fruit. Because both hickory and walnut nuts grow within an outer husk, some have called them drupes or drupaceous nuts, coining the specialized term "tryma" for such nut-like drupes. The Angiosperm Phylogeny Group, however, classifies the fruit simply as a nut.

Name, Nectar, and Neighborhood — Ecology and Cultural Echoes

The English word "hickory" is a clipped form of an Algonquian term—perhaps Powhatan—such as pockerchicory or pocohicora, which may have referred to the tree's nut or to a milky drink made from those nuts. The scientific genus name Carya comes from the Ancient Greek káryon, meaning "nut."

Beyond human use for edible nuts and timber, hickory plays a vital role in insect ecology. The leaves serve as food for the larvae of numerous Lepidoptera species, including the Luna moth, the Regal moth (whose caterpillars are popularly called hickory horn-devils), the Walnut sphinx, the Hickory tussock moth, and several others. A small insect called the hickory leaf stem gall phylloxera, a relative of aphids with a similarly complex life cycle, also feeds on the tree. Its eggs hatch in early spring, and galls quickly form around the developing insects. While these galls can damage weakened or stressed hickories, they are generally harmless, and the deformed leaves and twigs they produce often rain down from the canopy in spring.