Now that it is autumn, I am seeing fallen pignut hickory nuts in Sweetwater Creek State Park, on the campus of Youth Villages where I work, and in my neighborhood. The tree’s nuts are considered by some (but not all) to be bitter and good only for pigs and other animals to eat. The nuts are pear-shaped and somewhat flattened with a pointed end. The husk that does not separate easily from the nut makes the end not so pointed, and with the help of imagination some may resemble a pig’s snout. These associations of the tree’s nuts to pigs gives the tree its common name, but does not imply that the tree is inferior. Many animals and people eat the tree’s nuts, and the tree’s tough wood has valuable uses.
Less common names for the pignut hickory are smoothbark hickory and broom hickory. The bark is smoother than most hickories, and early settlers used the tree’s wood for broom and mop handles. Its scientific name is Carya glabra, with glabra referring to the tree’s smooth leaves. The pignut hickory prefers full sun or part shade, and humid climates. It is tolerant of both acid and alkaline soils, and its long tap root makes it tolerant of drought. It grows on dry ridgetops and slopes, and also on moist, well-drained sites. The tree is found through nearly all of the eastern United States, from Canada to central Florida, and westward into east Texas, Missouri, and extreme southeastern Iowa. It is said to have the greatest elevational range of any hickory in the Great Smoky Mountains, and to be the most dominant 
hickory species in the Appalachian forests. This species of hickory is common but not abundant in the Atlanta, Georgia area. Trees grow slowly and reach variable sizes, depending upon the favorability of sites and how long they are allowed to grow. An Atlanta Champion pignut hickory in Beecher Hills has height 145.4 feet, trunk circumference 6.7 feet, and spread 32.5 feet. Another in Glenn Lake Park, Decatur is shorter at 116.3 feet, but has trunk circumference 9.5 feet and spread 78 feet.
The pignut hickory has a rounded, oblong crown with coarse texture. Branches are strong, irregularly spaced and somewhat pendulous. The trunk tends to 
be straight and tall. Some trees I saw at Sweetwater Creek park were so tall that I had difficulty making out the number of leaflets on each rachis. Bark is smooth and light gray, and with maturity it turns darker and develops close and shallow, vertical furrows and scaly ridges that interlace in a defined “X” pattern. There are 3 or more overlapping scales on winter buds. Leaves are 8 to 12 inches long, and they are alternate and pinnately compound. A single leaf contains 5 and sometimes 7 ovate and serrate leaflets attached in opposite pairs to a long, slender and smooth rachis. The base 2 leaflets are about 1/3 the size of the upper 3 leaflets, and the end leaflet is the largest. The leaflets are dark green above and 
paler below, and are mostly smooth. Autumn color is golden yellow.
The pignut hickory begins to produce seeds after about 30 years, and can produce until it is about 300 years old. Male and female flowers of the pignut hickory are borne on the same tree. Female flowers are small, green, and in clusters of 2 to 5 on ¼ inch long spikes. Male flowers are drooping clusters of catkins averaging 2 to 3.1 inches in length. The fruit of the pignut hickory is technically not a nut but a drupe, because it has a kernel or seed surrounded by a shell surrounded by softer material. However, it is a nut in the culinary sense. The pignut hickory kernel is 
surrounded by a hard, thick, pear-shaped shell. This shell is not ribbed, is about .6 to 1.4 inches in length, and has the narrow end at the base. The husk has 4 ridges and is dark brown, smooth and thin. It is .18 inches or thinner. It does not separate easily from the shell, and splits at most half way when mature. It is usually easier to leave the husk on the shell when cracking for the kernel. Often, only half the nuts are found to be sound. Nuts that are not usable float in water, but this test is reliable only if the husk is removed. The kernel is varied in flavor, from sweet and flavorful to bitter and unpleasant.
Pignut hickory propagates by fallen seeds, and by 
sprouting of epicormic buds on root collars and stumps when trees have been cut or burned. Though animals spread seeds, the tree is slow to invade new areas. Interest in use of the trees for landscaping is low due to difficulty of transplantation due to the tap root, and its slow rate of growth. There is also low interest in use near roads, driveways, and sidewalks due to possibility of damage to vehicles from falling nuts and to pedestrians from losing balance rolling on the nuts.
The pignut hickory is useful for more than its nuts. It is used as a shade tree having little danger of limb breakage. The wood is heavy, strong, tough and 
elastic, and it is used where strength and shock-resistance is important. It is used for tool handles and agricultural implements, and for skis and other sporting goods. Other uses are for flooring, ladder rungs, wheel spokes and wagon wheels. The wood imparts flavor when used to smoke or cook meat. It is also a good fuel to burn in wood stoves, because it has a very high thermal energy content. Trees provide golden yellow color in autumn, and provide important food and shelter to wildlife.
When enjoying this tree in all its many ways, we should keep in mind that pignut hickory trees take a long time to reach their size, and are not easily replaced.