Bitternut Hickory
Carya cordiformis
Walnut family (Juglandaceae)

Description: This tree is 60-100' tall at maturity, forming a single trunk about 1-3' across and a variably shaped crown with ascending branches. In densely forested areas, the trunk is long and straight and the crown is relatively short; in open areas, the trunk is less long and the crown is relatively large and ovoid in shape. Trunk bark is highly variable, depending on the age of the tree: young trees have light gray to gray trunk bark with shallow fissures that are dull white or yellowish red; trees of intermediate age have trunk bark that is gray, rough, irregular, and shallowly furrowed; older trees have trunk bark that is gray with interlaced furrows and flat-topped ridges. Branches have bark that is gray and more smooth, while twigs are gray or light brown and glabrous. Young non-woody shoots are light green, terete, and glabrous; they have scattered lenticels that are white or pale yellow. Alternate compound leaves about 8-14" long occur along the twigs and young shoots; they are odd-pinnate with 7-9 leaflets (rarely 11 leaflets). The rachis (central stalk) of each compound leaf is light green and short-pubescent. The leaflets are 3-6" long and 1-2" across; they are elliptic, lanceolate, or ovate with serrated margins. Distal leaflets (farther from the petiole) are larger in size than proximal leaflets (closer to the petiole). Individual leaflets can be symmetric or asymmetric in shape (straight or slightly curved; more narrow on one side than the other). The upper surface of the leaflets is medium to dark green and glabrous, while the lower surface is pale green and pubescent along the veins. In addition, some short hairs or a sparse powdery coating may be located away from the veins across the lower surface. On each compound leaf, the leaflets are sessile or nearly so, although the terminal leaflet sometimes has a short petiolule (basal stalklet) about 1/8" (3 mm.) long.

During most of the year, the terminal and lateral buds on young twigs and shoots are bright sulfur-yellow or yellow-orange from a powdery coating. Each bud has 2 valvate (non-overlapping) scales. Bitternut Hickory is monoecious with both male and female flowers produced on the same tree. The male flowers are arranged in greenish yellow catkins that are 3-5" long; these catkins are arranged in clusters of 3, drooping downward from either the tips of the previous year's twigs or at the base of the current year's twigs. Each tiny male flower has a 3-lobed calyx and several stamens. The female flowers are arranged in small short spikes at the tips of the current year's twigs. Each female flower is about 1/8" (3 mm.) long, consisting of an ovoid ovary with 4 prominent ridges and a pair of styles. The blooming period occurs from mid- to late spring for about 1-2 weeks. The flowers are cross-pollinated by the wind. Fertile female flowers are replaced by ovoid-globoid fruits (nuts with thin greenish husks) that become about 1" long at maturity during the autumn. Each husk has a smooth surface with 4 narrow ridges that extend from the outer tip inward to about one-half to two-thirds of the fruit's length. At maturity, the husk splits open along these ridges to partially release the nut. Each nut has a round circumference with a prominent beak; its shell is light brown, thin, and relatively smooth. The meat of the nut is very bitter. The root system has a taproot with spreading lateral roots.

Cultivation: The preference is full or partial sun, moist to dry-mesic conditions, and a fertile loamy soil, although less fertile gravelly soil is tolerated. Individual trees can live up to 200 years; they have to be at least 30 years old to produce nuts.

Range & Habitat: The native Bitternut Hickory occurs in every county of Illinois; it is fairly common (see Distribution Map). This tree is usually found in bottomland woodlands, protected river valleys, and even drier areas of swamps; it also occurs in upland woodlands, along the edges of rocky glades, woodland borders along roads, and edges of powerline clearances in wooded areas. It is somewhat vulnerable to fire and can be found in both degraded and higher quality woodlands.

Faunal Associations: Many insects bore through the wood, suck plant juices, or feed on the foliage and other parts of Carya spp. (hickory trees). These insects include caterpillars of the butterflies Satyrium calanus falacer (Banded Hairstreak) and Satyrium caryaevorum (Hickory Hairstreak); this last insect has been observed to feed on Bitternut Hickory specifically. The caterpillars of Lophocampa caryae (Hickory Tussock Moth), Catocala nebulosa (Clouded Underwing), Catocala subnata (Youthful Underwing), and other moths also feed on hickory trees (see Moth Table); the monophagous moth, Youthful Underwing, is supposed to feed on the foliage of Bitternut Hickory exclusively. The larvae of Goes pulcher (Living Hickory Borer), Megacyllene caryae (Painted Hickory Borer), Saperda discoidea (Hickory Saperda), and other long-horned beetles bore through the wood of hickory trees; other wood- or bark-boring beetles include Scolytus quadrispinosus (Hickory Bark Beetle) and Chrysobothris adelpha. The larvae of Conotrachelus aratus (Hickory Shoot Curculio) bore through new shoots, while the larvae of Conotrachelus hicoriae (Hickory Nut Curculio) bore into the nuts of hickories. Other insect feeders include aphids, treehoppers, leafhoppers, plant bugs, and other species; Bitternut Hickory is the preferred host of the leafhopper Erythridula ampla (syn. Erythroneura ampla). See the Insect Table for a more complete listing of these insect feeders.

Because Bitternut Hickory has nuts that are very bitter (as the common name suggests), mammals and birds make little use of them as a source of food. However, White-Tailed Deer browse occasionally on the saplings, twigs, and foliage of this tree, Cottontail Rabbits browse on the seedlings, Meadow Voles feed on the bark of saplings during the winter, and Beavers use the branches and wood of trees that grow near sources of water. Woodpeckers, warblers, and other insectivorous birds search for insects and their larvae in the wood or among the leaves of this and other hickories; these trees also provide protective cover and nesting habitat for many birds.

Photographic Location: Along a roadside at Busey Woods and at the Arboretum of the University of Illinois in Urbana, Illinois.

Bitternut Hickory has a wider range and it is found further north than any other hickory tree. It belongs to a group of hickories that are known as the 'Apocarya.' Hickories in this group have non-overlapping yellowish buds, strongly ridged fruits, abundant leaflets (typically 7-19 per leaf), and non-shaggy bark. Rather oddly, Bitternut Hickory is closely related to the Pecan (Carya illinoensis), even though their nuts are at opposite extremes in terms of their palatability (very bitter vs. mild & sweet). In Illinois, Bitternut Hickory can be distinguished from other hickory trees by its bright sulfur-yellow buds, which are covered by a powdery coating. It also has smaller fruits (husked nuts) than most hickory trees. Its nuts are rounded rather than angular, and they have large terminal beaks. While the husks of Bitternut Hickory have 4 narrow ridges that extend inward to about one-half to two-thirds the length of its fruits, other hickory trees have husks that either lack ridges or their ridges extend the complete length of their fruits. Pignut Hickory (Carya glabra) has fruits that are similar in size to those of Bitternut Hickory, but they lack conspicuous ridges; this tree also has fewer leaflets (usually 5) per compound leaf and its buds aren't yellow. The Pecan is also similar to Bitternut Hickory in several respects, but it has more leaflets (9-17) per compound leaf. Furthermore, Pecan has fruits with a more elongated shape, they are longer in length (exceeding 1"), and each of its fruits has ridges that extend from one end to the other.