The genus of hickory includes 17-19 species of deciduous trees, mostly occurring in eastern North America with a remaining few species native to southeastern Asia and Mexico. Characteristic of many eastern hardwood forest types, the hickories are all larger trees. Relatively long-lived, they can be found across a range of topography and soil types, with individual species having a strong preference for one type in particular. Often found in association with each other wherever their ranges overlap, naturally occurring hybrids are common. Intermediately shade-tolerant, hickories range from being slow-growing to moderately quick.
The leaves are alternately arranged and, like the walnut, pinnately compound with five to eleven leaflets depending on the species. The flowers are tiny, without petals, and inconspicuous emerging with the leaves in spring. Male flowers are born in loose three-branched catkins at the end of branches with the female flowers in small clusters at the ends of others. They are self-incompatible and like other catkin bearing trees, wind-pollinated. The fruit is a large nut within a relatively thick husk that usually splits when ripe. The shell is thick and bony in most species, and thin in a few. In a number of species, most notably the Pecan, the seed inside of the nut is edible. There is a great variability in flavor from one cultivar to the next; however, they are all high in unsaturated fat with strong medical antioxidant properties. Members of the Walnut Family, Hickories are an economically important group of trees. Not only valued for their palatable seed harvests, several species of hickory wood are prized for being hard and impact-resistant. Some hickories also make wonderful shade trees on suitable larger sites, their fall colour usually an excellent warm, antique gold.
In the natural state of hardwood forests, hickory trees have hybridized easily and readily within the species to produce a multitude of variations and expressions of characteristics that possess the traditional vigor of the tree. One notable example of this is a natural hybridization between Shagbark Hickory and Pecan. The resulting nuts seem to have flavor and characteristics somewhere between the two species and has started to become popular with nut hobbyists under the moniker ‘Hican.’
Carya illinoensis Hickory Pecan
Arguably the most economically important food crop native to North America, its noncommercial range encompasses the bottomlands of the Mississippi River, from Indiana through Illinois and south to the Gulf of Mexico where it can be found in the surrounding mountains. The Pecan has a strong preference for well-drained loamy soils and is largely limited throughout its range to the sediment of rivers and streams where it is not subject to too much flooding.
A large deciduous tree, growing to heights of 130 ft (40 m) during its lifetime, Hickory Pecan may live and bear edible seeds for more than 300 years, producing on average 100 pounds (40kg) of nuts each year. It is usually a single-trunked tree, with a number of large ascending limbs that develop into an irregular crown. Their leaves are alternately arranged in the typical pattern for hickories and reach lengths of 20 in (50 cm). The flowers are wind-pollinated catkins, the male flowers of which cluster into pendulous groups up to 7 in (18 cm) long. The nuts are typically harvested around mid-October.
The wood of Hickory Pecan has a golden to creamy colour, with reddish heartwood. It is close grained, dense, and very hard; one of the hardest woods readily available making it especially suitable for many applications. A number of finishes can be used, as the wood takes stain well after drying.
Carya ovata Shagbark Hickory
With an extensive range throughout North America this species of hickory can be found anywhere east of Texas and Minnesota and as far north as southern Quebec. It is its distinctive, shaggy bark, conspicuous on tall straight trees, which gives the species its name. However the bark does not begin to shred until the tree is about 25 years and until then has a shiny, smooth bark. Growing best in humid climates on rich, deep, moist soils of various composition, this fairly shade tolerant tree is found in many mixed hardwood forests. Moderately long lived, the Shagbark Hickory reaches 80 ft (25 m) during its 200 years, with a single dominant trunk that penetrates the canopy. When open grown the crown is broadly oblong, but tends to be narrow and columnar in forested conditions.
The five to seven leaflets form the typical hickory leaf 10 in (25 cm) in length, which turn the typical rich gold in autumn. The fruit of this hickory is generally borne in clusters of two or three at the ends of branches. Round and smooth with grooved sutures where the husk splits when ripe, releasing a light beige, four-ridged nut containing an edible seed.
A commercially important tree for its timber and its seed, the wood is regarded the best of the hickories. Tough, hard and resilient this wood is known for its impact and stress resistance and is widely used for furniture, flooring, tools, sporting equipment and a variety of other implementations.
Carya laciniosa Shellbark Hickory
Also known as Kingnut for having the largest fruit of any hickory, this deciduous tree prefers wet, fertile bottomland and like other hickories is very tolerant of summer drought. Similar to the Shagbark species, but not quite so shaggy it is less common than either Shagbark or Bitternut species. The wood is similar to Shagbark in that it is highly impact and stress resistant and is used much in the same way. Shellbark is a heavy, dense, strong yet elastic wood that is sought after for a number of uses.
Carya tomentosa Mockernut Hickory
Reaching heights of 100 ft. (30 m), this single -trunked tree attains its best growth on fertile, deep upland soils ranging from Massachusetts to Florida and eastern Texas. In the south is may also be found on moist bottomlands, and in the north preferring rocky, sandy slopes and hill-sides. It is often found in association with a variety of other hardwood trees and pines. The typical hickory-type leaves are 20 in (50 cm) long and composed of seven or nine leaflets. The fruit is brown and roughly elliptical with a thick husk.
The wood is hard, tough, and strong. The heartwood is a brown or reddish colour. Typically straight grained, but can be wavy or irregular and the texture is somewhat coarse. The strength of the lumber depends on varying rate of growth and can be difficult to work with while still taking a good finish.
Carya glabra Pignut Hickory
This tree grows well in fairly rich, well drained to dry souls and occurs with other hickories and oaks, characteristically on hillsides and ridges. The fruit of this hickory is particularly bitter and as a food source, only important for foraging wildlife. Shallow furrows and ridges in a semi diamond pattern may mark the firm, grey bark of this species. It has medium-green broad, flat leaves which turn a bright yellow for fall. As with other hickories, the wood of this variety is tough and strong.
Carya cordiformis Bitternut Hickory
Also known as the Yellow-bud Hickory, as it is this expression that makes it easy to distinguish from other species. Combined with the alternate compound leaves and relatively large nuts it is a distinctive tree. The lighter coloured shallow cracks in the younger bark are similar to those of young Shagbark Hickory, but the mature bark does not split so deeply as its kin.
Found on moist, fertile soils in the east and central US this species of hickory is shade intolerant and is not found at high altitudes. This fast growing, adaptable tree is best known for its hard wood and forms a broad crown when open-grown. A single-trunked tree, the Bitternut often grows to 80 ft (24 m) and the pinnately compound leaves typically have seven or nine stalkless leaflets that turn a rich yellow-gold in autumn.