Identify Common Major Hickory Species in North America

Hickory Trees in the Walnut Family: Juglandaceae

Old Hickory
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Trees in the genus Carya (from Ancient Greek for "nut") are commonly known as hickory. The worldwide hickory genus includes 17–19 species of deciduous trees with pinnately compound leaves and large nuts. North America has the overwhelming edge on the number of native hickory species, with a dozen or so (11–12 in the United States, one in Mexico), while there are five or six species from China and Indochina. The hickory tree, along with the oaks, dominates the hardwood forests of eastern North America.

Identifying the Common Hickories

There are six species of Carya that make up the most common hickories found in North America. They come from three major groups called shagbark (which has shaggy bark), pignut (which rarely has shaggy bark), and the pecan group. The shaggy bark is a clear identifier to separate the shagbark group from the pignut group, though some older hickories have slightly scaly bark.

Hickories have a nutritious nut meat that is covered by a very hard shell, which is in turn covered by a splitting husk shell (as opposed to a larger walnut that drops with a complete husk cover). This fruit is located at the twig tips in clusters of three to five. Search for them for under a tree to help in identification. They have branching flowering catkins just below the emerging new leaf umbrella-like dome in spring. Not all are eaten by humans.

The leaves of hickory are mostly alternately placed along the twig, in contrast to a similar-looking ash tree leaf that is in an opposite arrangement. The hickory leaf is always pinnately compound, and the individual leaflets can be finely serrated or toothed.

Identification While Dormant

Hickory twigs have tan, five-sided or angled soft centers called piths, which are a major identifier. The tree's bark is variable along species lines and not helpful except for loose, flaky bark on the shagbark hickory group. The tree's fruit is a nut, and splitting husks are often visible under a dormant tree. Most hickory species have stout twigs with large terminal buds.

Growing North American Hickory Species

These large, long-lived, slow-growing deciduous trees are known for being good shade trees and feature golden color in the fall. They are difficult to transplant because of their long taproot and might be hard to find in nurseries. Their bark is a range of gray colors, whether they have shaggy bark or not, and you'll find them in USDA Zones 4–9, though the pecan is found in Zones 5–9. Fruit drops from late summer into autumn.

Shagbark hickory, Carya ovata, is as you would imagine, a tree with shaggy bark that peels away in big pieces. Their mature height is 60–80 feet tall, with a 30–50-foot width. Leaves are 8 to 14 inches long, with five to seven leaflets These trees are tolerant of a wide range of conditions, such as drought, acidic or alkaline soil, but do need a well-drained, large location free from salty soil. The round nut has a four-sectioned husk.

The shellbark hickory, Carya laciniosa, is a shaggy gray-bark species. This hickory grows up to 75–100 feet tall with a 50–75-foot width. It's not tolerant of alkaline soils or drought conditions, salt spray or salty soils and needs a big area of well-draining soil. It's best grown in moist soils. Leaves are in clusters of seven to nine leaflets. Oval nuts have a five- to six-sectioned husk and are the largest of the hickory species.

The mockernut hickory, Carya tomentosa, reaches 50–60 feet tall and 20–30 feet wide. It's tolerant of drought but not poor drainage and is best in slightly acidic soil, as it's intolerant of alkaline soils and salt in the soil. Its leaves are alternate, compound leaves with seven to nine leaflets that are hairy on the underside and the stalk; the largest will be the terminal leaf. Its nuts ripen in fall and have four sections.

The pignut hickory, Carya glabra, is a dark-gray tree that extends to 50–60 feet in height with a spread of 25–35 feet. It does well in a variety of soils. It moderately tolerates salty soil and hangs in there through drought, but it doesn't do well in areas of poor drainage. As the tree ages, the bark may appear slightly shaggy. Its alternate, compound leaves are 8 to 12 inches long with five to seven leaflets, with the one on the end being the largest. The bitter nuts are pear-shaped and have four ridges on the husks, which do not easily come off of the nut.

The pecan tree, Carya illinoinensis, contains the sweetest nuts of all the hickory trees and is one of the most important native North American nut trees, though it can be a messy tree to grow due to leaf and fruit drop. It grows 70–100 feet tall with a spread of 40–75 feet. It's tolerant of acidic soils and only moderately tolerant of alkaline soils. It'll handle some poor drainage all right but not drought, salt spray, or salty soil. The bark is brownish black, and leaves are 18–24 inches long, containing nine to 17 narrow, long leaflets with a hook shape near each tip. Nuts are cylindrical.

The bitternut hickory, Carya cordiformis, also commonly called the swamp hickory, loves moist conditions and hates drought and poor drainage, though it can be found in some drier landscapes in addition to its typical low, wet conditions. It needs a large area to grow and can reach 50–70 feet high and 40–50 feet wide when mature. It prefers acidic soil but can tolerate alkaline. It can handle some salt spray but not salty soil. Leaves contain seven to 11 long, narrow leaflets.

It grows bitter nuts that, although not poisonous, to humans are more of the inedible variety due to their taste. The nuts are about an inch long and have four-sectioned, thin husks. To identify the tree in winter, look for its bright yellow buds.