The Hickories – Carya sp.

While oaks may be our primary focus at Starhill Forest Arboretum, we could hardly call ourselves stewards of an oak-hickory forest without giving the genus Carya—the hickories—a strong presence in our collection.

The genus Carya includes nearly 20 species worldwide. The hickories are known for their strong, useful wood prized for furniture and flooring, as well as their beauty and usefulness as wildlife habitat. Thirteen of these are native to North America, and nearly all are represented in our living collections. While a few species are found in eastern and southeastern Asia, it’s unlikely they would survive our Midwestern winters.

Most North American hickory species occur in Illinois. Shagbark hickory (Carya ovata) is one of the most recognizable, with its signature peeling bark, while shellbark hickory (C. laciniosa) is often mistaken for shagbark due to its similar bark, though it is more commonly found in wetter bottomlands. Mockernut hickory (C. tomentosa) is identified by its thick, hairy twigs and leaves. Pignut hickory (C. glabra) and sweet pignut (C. ovalis) are often treated as separate species, though some taxonomists consider C. ovalis a variety of glabra. Bitternut hickory (C. cordiformis) is the most widespread and northern species, while black hickory (C. texana) has a more limited range, occurring on poor soils, in sandy or rocky conditions. Pecan (C. illinoinensis) is a particularly prized edible hickory. The genus is typically divided into the “true hickories” and the “pecan hickories,” with the latter group including both the bitternut and pecan.

Keys to identification: When identifying hickories, it’s helpful to focus on a few key traits. Most species have compound leaves with 5 to 9 leaflets, often serrated along the edges, and the twigs are sturdy with prominent buds that can be rounded, scaly, or even hairy depending on the species. Bark is another important feature—shagbark hickory, for example, is well-known for its long, peeling strips, while bitternut tends to have smoother, tighter bark. Nuts provide additional clues: some, like pecans, have thin shells and sweet kernels, while others, such as mockernut or bitternut, have thick, hard shells or bitter seeds. Habitat can also narrow down the possibilities, since certain species prefer upland sites with dry soils, while others, like shellbark and pecan, are more common in bottomlands and river valleys. Together, these characteristics—leaves, buds, bark, nuts, and habitat—make it possible to distinguish one hickory species from another. This chart from the University of Illinois Extension is a useful tool, listing each species with its associated identifying characteristics. Since you often need to take multiple characteristics into account, the hickories are one group that we might not trust the AI apps for correct ID beyond genus!

On the Arboretum grounds, shagbark and bitternut hickories occur naturally. The bitternut’s small, bitter nuts are easy to spot underfoot, especially along our trails—less popular with wildlife, but much more abundant as a result! Shagbarks, on the other hand, are prized by squirrels and other critters, so collecting their nuts takes strategy (and speed!).

Our curated collection includes 35 specimens representing 11 species and one hybrid. Some of our oldest trees trace back to seed collected in the early 1970s, including a shellbark hickory from near Ferne Clyffe State Park (Accession #1981-004) and our only living sweet pignut, likely gathered during the same trip near Vienna, Illinois. Water hickory (C. aquatica) is another interesting species in our collection. It is primarily a Gulf coast species, though populations can be found along the Missisissippi River valley, just reaching Illinois’ southernmost counties. Our oldest specimen hails from the Cache River (#1981-002) and more recently, we’ve added the species from Georgia sources.

Thinking of Planting One? Start Small.

Hickories are notoriously tricky to transplant due to their deep taproots, which form early. Even though their top growth can seem slow, these trees are hard at work underground. At Starhill, we rarely leave a hickory seedling in the nursery or a container for more than two years for this reason.

If you’re planting one at home, be mindful of placement: while beautiful, hickories produce large nuts that can dent cars or become a hazard near sidewalks. On the bright side, if you pick a species favored by wildlife, nature will help with the cleanup. We usually find the husks and shells reduced to a fine mulch!

Hickories are also among our most striking trees in autumn, with many species turning a rich golden yellow. With part of our collection lining the main drive, their fall color is impossible to miss—especially when backlit by the late afternoon sun.

Hickories and Wildlife

Hickories support an impressive range of wildlife. Many insects feed on their wood, leaves, and sap, including beetles, weevils, aphids, leafhoppers, moths, butterflies, and more, with some species—such as several underwing moths—feeding almost exclusively on Shagbark Hickory. The sweet nuts of hickories are important food for squirrels, chipmunks, raccoons, mice, deer, and numerous bird species, which also help disperse the seeds. Deer browse lightly on the foliage, while rabbits sometimes gnaw the bark of young trees. Because hickories host so many insects, they attract a variety of insect-eating birds, and Shagbark and Shellbark Hickory’s peeling bark and cavities provide valuable shelter. These bark crevices are used as roosts by bats, and as nesting or roosting spots by birds like woodpeckers and owls, making hickories vital to many forest species.

Where to See Hickories at Starhill

If you’re visiting the Arboretum, hickories are easy to find in several areas. Many mature specimens line the main driveway on our west hill, where their golden fall color really shines. Another concentrated planting can be found just south of the Catalpa House, where a variety of species are growing together.

Beyond the curated collection, spontaneous hickories—especially bitternut and shagbark—can be found in the woods around and below the pond, contributing to the natural oak-hickory woodland character of the site.

Follow Along—We’ll be sharing more photos, facts, and stories about hickories in our collection—and some of the remarkable specimens we’ve come across elsewhere—on our Facebook page. Follow us and join the conversation as we continue to celebrate this important native genus.