Walnut family (Juglandaceae)
Description: This tree is 70-150' tall at maturity, forming a trunk 2-6' across. In open areas, the trunk is relatively short, while the crown has a globoid form from widely spreading branches. In forested areas, the trunk is relatively longer and the crown is more narrow. Trunk bark of mature trees is gray to gray-brown and rough-textured; it has shallow irregular furrows and flattened ridges with barely discernible shapes. The bark of large branches is similar to trunk bark. Small branches are gray and smooth, while young twigs are brown and usually pubescent. Alternate compound leaves 1-2' long develop along the twigs; they are odd-pinnate, consisting of 9-17 leaflets. The leaflets are 2-7" long and ½-2½" across, lanceolate or lanceolate-oblong in shape, curved to one side, and coarsely serrated along their margins. The leaflets have asymmetric bases and elongated tips. Their upper surfaces are yellowish green to dark green and glabrous, while their lower surfaces are pale green and glabrous to sparsely pubescent. The petiolules (small stalklets at the bases of leaflets) are light green, usually pubescent, and short (about ¼" long). The central rachis (stalk) and petiole of each compound leaf are light green and usually pubescent.
Pecan is monoecious with both staminate (male) and pistillate (female) florets on the same tree. Short pistillate spikes develop at the tips of some twigs; each spike has 2-10 greenish pistillate florets. Individual pistillate florets are about 1/4" (6 mm.) long and 1/8" (3 mm.) across, consisting of a short tubular calyx, 4 bractlets of unequal size, and a pistil. The bractlets have 4 erect to spreading lobes that are lanceolate in shape. Drooping staminate catkins about 4-6" long develop from short spurs along the twigs; these catkins are yellowish green and usually occur in groups of 3. Individual staminate florets have a 3-lobed bractlet and 4-6 stamens; the central lobe of the bractlet is longer than the lateral lobes. The blooming period occurs from mid- to late spring for about 2 weeks. The florets are cross-pollinated by the wind. During the summer, fertile pistillate florets are replaced by clusters of 1-6 fruits (nuts with thin husks). These fruits are about 2" long, 1" across, and ovoid-oblongoid in shape. Along the length of each fruit, there are 4 short wings. The husk surface is smooth and hairless; it is initially light green, but later becomes brown or black. A mature fruit partially divides into 4 segments (along its wings) to release the nut. The nut surface is light brown and smooth; the interior of the nut has sweet edible meat. This tree reproduces by reseeding itself.
Cultivation: The preference is full or partial sun, moist conditions, and a fertile loamy soil. The leaves develop relatively late in the spring, but remain green into the fall before turning yellow. Allow plenty of room for development: Pecan can become a big tree with a life expectancy that may exceed 300 years.
Range & Habitat: Pecan is a native tree that is occasional in southern and western Illinois (see Distribution Map). Habitats consist of rich mesic woodlands, moist bottomland woodlands in river valleys, and tree plantations. Pecan is typically found with other bottomland deciduous trees along major river valleys. This tree is cultivated commercially for its valuable nuts; less often it is cultivated as a landscape plant.
Faunal Associations: The following moth caterpillars have been observed to feed on Pecan: Actias luna (Luna Moth), Catocala maestosa (Sad Underwing), Catocala piatrix (The Penitent), Catocala vidua (Widow Underwing), Datana integerrima (Walnut Caterpillar), and Lophocampa caryae (Hickory Tussock Moth). Other insects that feed on Pecan include: the aphids Longistigma caryae, Monellia caryella, and Monelliopsis nigropunctata; the plant bugs Lygocoris caryae, Orthotylus ramus, and Plagiognathus albatus; the leafhoppers Eratoneura osborni and Erythridula cauta; the treehopper Carynota mera; and the leaf beetle Metachroma marginale. In addition to these species, many other insects are known to feed on Carya spp. in general. Among vertebrate animals, Pecan nuts are an important source of food. They are eaten by the Wood Duck, Wild Turkey, Red-Bellied Woodpecker, Gray Squirrel, Fox Squirrel, Southern Flying Squirrel, Eastern Chipmunk, White-Tailed Deer, Black Bear, and White-Footed Mouse. White-Tailed Deer also browse on the twigs and leaves. The tree sap of Pecan is a source of food to the Yellow-Bellied Sapsucker. This tree provides good cover for various kinds of wildlife; the Scissor-Tailed Flycatcher and other birds sometimes construct nests in its branches.
Photographic Location: The Arboretum at the University of Illinois in Urbana, Illinois.
Comments: Pecan is renowned for its tasty nuts, which are used primarily in desserts. This tree is in the same genus as the hickories (Carya spp.) and it occasionally forms hybrids with some of these species. Compared to other Carya spp., Pecan has more leaflets (9-17) per compound leaf and its fruit is more elongated in shape (about twice as long as it is across). It is possible to confuse Pecan with Juglans nigra (Black Walnut) and Juglans cinerea (Butternut) because they have a similar number of leaflets, but the husks of their fruits do not divide into 4 segments and they also lack wings. Unfortunately, multiple spellings of the scientific name for Pecan are currently in use: Carya illinoensis, Carya illinoiensis, and Carya illinoinensis. Without examining the original manuscript that introduced the current scientific name, it is difficult to determine which spelling is correct. The spelling in Mohlenbrock (2002) has been used here.