How to distinguish American chestnut trees from other chestnuts within the original native range, with information on other chestnut species.
Chestnuts have been cultivated for nuts and wood for thousands of years. The name Castanea is believed to come from Kastanea, a city in Pontus, Turkey. European chestnuts (Castanea sativa) probably originated in Southern Russia in the Caucasus mountains, between the Black and the Caspian Seas. They were planted throughout the Roman Empire, and now grow wild in Italy, France, Spain, and Greece. Chestnuts are also important in Asia, where there are four native species (Castanea mollissima, C. Henryi, C. seguinii, and C. crenata).
In North America, pollen records from the latest interglacial period show that the American chestnut tree, Castanea dentata, was present on Long Island 30,000 to 50,000 years ago. American chestnut trees were once found all along the Appalachian mountain range, from Portland, Maine to northern Georgia. Within this area it grew in mixed, hardwood forests, usually on high, sandy land, gravel ridges, or mountain slopes that were wholly, or nearly free from limestone. In the last 150 years it has been planted outside its range in favorable spots (Michigan, Wisconsin) where it has become a forest tree, protected from chestnut blight disease by geography until only recently. American chinquapins, Castanea pumila, share the southern part of the range with American chestnut from Pennsylvania south.
Chestnuts are deciduous trees with short-stemmed, prominently veined, oblong leaves that have course to fine pointed marginal teeth or bristles. Male (staminate) flowers are formed in the axils of successive or alternate leaves in early June, in groups of cylindrical catkins (aments) as long as or longer than the leaves. Female (pistillate) flowers form later and on younger wood, at the base of short catkins. The nuts develop in prickly husks called burs (with one r), which open when the nuts are mature (usually mid-September to mid-October).
There are seven species identified by taxonomists, and the following key is intended to separate them.
Leaves to be examined should be fully expanded, from parts of the tree exposed to full sun, and not from within 6 inches of flowers.
Leaves hairless, or with only a few, short hairs on the mid-vein on the lower surface.
A. Nuts usually 1 to 3 per bur (but sometimes as many as 7 to 10), leaf margins deeply indented.
1. Twigs smooth, lower surface of fully expanded leaves with few
glands, leaves 5 to 10 inches long.
Castanea dentata (Marshall) Borkhausen American chestnut
Before ink disease and chestnut blight disease were brought into the US, this was a tree 60 to 80 (occasionally 100) feet tall. Now mature trees are uncommon within the native range, and the species is usually found as a shrubby cluster of sprouts 3 to 15 feet tall, or as an understory tree 15 to 60 feet tall. The twigs are chestnut brown, the buds are smooth and brown and asymmetrically bullet-shaped, usually askew on the twig. Leaves are oblong, pointed at the tip, and acute at the base where they join the petioles (i.e., are canoe shaped), with coarsely dentate (toothed) margins. Mature leaves are light green and paper-thin.
The most striking difference between American chestnut trees and the other species is their slender, upright growth, and their thinner, smoother leaves, which are more pendent in position. The nuts are generally smaller than all other chestnuts, except chinquapins, and are sweeter.
2. Twigs with short, simple hairs, lower surface of fully expanded
leaves densely covered with glands, leaves 2 to 4 inches long.
Castanea seguinii Dode Dwarf Chinese chestnut
This species is a shrub to a small tree in China, but is not very winter-hardy in Connecticut. It seems to have little resistance to chestnut blight disease. Flowers form early in the spring and continue to form through the growing season, until killed by the first frost. Hybrids are valuable for use as dwarfing rootstocks, and for their ever-flowering characteristic.
B. Nuts usually one per bur, leaf margins with bristle-like teeth, leaves shaped like willow leaves, and 3 to 6 inches long.
Castanea Henryi (Skan) Rehder and Wilson Chinese chinquapin
I know of only one mature Henry chestnut in Connecticut, and this tree (in
our Plantation) is not reliably winter-hardy and not very resistant to chestnut blight. Trees in western Georgia have little blight and appear to resist Oriental Gall Wasp. Reports from China suggest that the tree is used for timber in that country.
Leaves hairy on the lower surface, and nuts usually 1-3 per bur.
A. Twigs thick and coarse, brown and downy at first, and then becoming smooth, leaves 5 to 10 inches long with long hairs on veins of both the lower and upper surfaces.
Castanea sativa Miller European chestnut
These trees were extensively planted in North America, starting in 1773 (Thomas Jefferson). The commercial nuts of France and Italy are cultivars called 'Marrone' that are probably European X Asian hybrids. 'Marrone' have stellate hairs on the lower surface of the leaves, and are male sterile. They were selected by Monks in what is now Turkey in the 1100's. 'Marrone' are usually apple-like, orchard trees, grafted on European rootstocks, and their nuts are large.
Trees of the pure species are tall and straight like American chestnut trees. Leaves are usually not acute where they join the petiole, and have no stellate hairs. Nuts of the pure species are about the size of American chestnuts. Both types of trees are very susceptible to chestnut blight, and are usually not very winter-hardy. There were many hybrids of C. sativa X C. dentata planted in the US in the last century, including the popular cultivar 'Paragon'.
B. Twigs greenish brown and downy, leaves coarsely serrate with dense or sparse stellate hairs on the lower surface, leaves usually thick and leathery.
Castanea mollissima Blume Chinese chestnut
Both orchard and timber trees have been extensively planted in
North America since about 1915. Nuts are small to large, and often quite sweet. Chinese chestnut trees range in resistance to chestnut blight from very susceptible (as susceptible as American chestnut trees) to very resistant. Many cultivars are very cold tolerant.
C. Twigs delicate, dark, reddish brown, and downy, becoming smooth as they mature, leaves with dense or sparse stellate hairs on the lower surface, leaf margins with bristle-like projections instead of deeply cut teeth.
Castanea crenata Siebold and Zuccarini Japanese chestnut
The trees extensively planted in North America, since 1876, were predominately orchard trees. They are usually very resistant to chestnut blight and ink disease, and some cultivars have been selected for their resistance to Oriental Chestnut Gall Wasp. The nuts are medium to very large, and often bitter when fresh.
Leaves densely hairy on the lower surface, and nuts always single in the burs.
Castanea pumila (Linnaeus) Miller
var. pumila Allegheny chinquapin
var. ozarkensis (Ashe) Tucker Ozark chinquapin
Chinquapins can be small, multi-stemmed shrubs, or single-stemmed trees 60 feet tall. The taxonomy of the group is still in flux, but other types described in the older literature include C. ashei, C. alnifolia, and C. floridana. They are all very susceptible to chestnut blight disease, but Allegheny chinquapins have been reported to be resistant to the Oriental Chestnut Gall Wasp.
Charles and Lina Rhora
Wainfleet, Ontario, Canada LOS 1VO
Sandra L. Anagnostakis is President of NNGA and a researcher specializing in Chestnuts at The Connecticut Agricultural Experiment Station. She can be reached at Sandra.Anagnostakis@ct.gov