Carpinus caroliniana

American Hornbeam

Alternate Names

Ironwood, musclewood, muscle beech, blue beech, water beech

Uses
The wood of Carpinus is of minor economic importance because of the small size of the trees. It is whitish, extremely hard, and heavy and has been used for making mallet heads, tool handles, levers, and other small, hard, wooden objects. The wood is not subject to cracking or splitting and was used by American pioneers for bowls and dishes. American hornbeam is planted in landscapes and naturalized areas. It prefers deep, fertile, moist, acidic soil and grows best in partial shade, but will grow in full sun. Its chief liabilities in cultivation are a relatively slow growth rate and difficulty in transplantation. It is not drought-tolerant.

Seeds, buds, or catkins are eaten by a number of songbirds, ruffed grouse, ring-necked pheasants, bobwhite, turkey, fox, and gray squirrels. Cottontails, beaver, and white-tailed deer eat the leaves, twigs, and larger stems. Beaver heavily uses American hornbeam, because it is readily available in typical beaver habitat.

Description

General: Birch Family (Betulaceae). American hornbeam is a native, large shrub or small tree with a wide-spreading, flat-topped crown, the stems slender, dark brown, hairy; bark gray, thin, usually smooth, with smooth, longitudinal fluting (resembling a flexed muscle). Its leaves are deciduous, simple, alternate, ovate to elliptic, 3-12 cm long, with doubly-serrate edges, dark green, turning yellow to orange or red in the fall, glabrous above, slightly to moderately pubescent beneath, especially on major veins, with or without conspicuous dark glands. The flowers are unisexual, in catkins, the male (staminate) catkins 2-6 cm long, female (pistillate) catkins 1-2.5 cm long, both types on the same plant (the species monoecious). Fruits are a nutlet 4-6 mm long, subtended by a 3-winged, narrow, leaf-like bract, numerous nutlets held together in pendulous chain-like clusters 2.5-12 cm long, changing from green to brown in September-October. The common name, beam, is an Old English word for tree, with horn suggesting an analogy of the hard, close-grained wood to the tough material of horns.

Variation within the species: the two subspecies are distinguished by morphology and geography. They hybridize or intergrade where their ranges overlap in a broad band running from the Carolinas south to northern Georgia and westward to Missouri, Arkansas, and southeastern Oklahoma. Plants with intermediate features are also found throughout the highlands of Missouri and Arkansas.

1. Leaf blades narrowly ovate to oblong-ovate, 3-8.5(-12) cm long, acute to obtuse at the tip; secondary teeth blunt and small; lower surfaces without small dark glands; southern Atlantic and Gulf of Mexico coastal plains and also extends northward in the Mississippi Embayment. ............. subsp. caroliniana

2. Leaf blades ovate to elliptic, mostly 8-12 cm long, usually abruptly narrowing at the tip, sometimes long and gradually tapered; secondary teeth sharp-tipped, often almost as large as primary teeth; lower surfaces covered with tiny, dark glands; Appalachians and interior forested northeastern North America.

Trees of temperate forests in the mountains of Mexico and Central America, formerly considered to be part of Carpinus caroliniana, are now treated as C. tropicalis (J.D. Smith) Lundell spp. tropicalis and C. tropicalis ssp. mexicana Furlow.

Distribution: Widespread in the eastern United States --- from central Maine west to southwestern Quebec, southeastern Ontario, northern Michigan, and northern Minnesota, south to central Iowa and eastern Texas, east to central Florida. Absent from the lowermost Gulf Coastal Plain and the Mississippi embayment south of Missouri).
Adaptation

American hornbeam occurs primarily as an understory species in bottomland mixed-hardwood forests. Best sites are in the transition between mesic and wet areas -- near lakes and swamps, on well-drained terraces of rivers, terraces or steep slopes of minor streams with some gradient, coves, ravine bottoms, and rises in lowlands. These sites generally have abundant soil moisture but sufficient drainage to prevent saturation and poor aeration during the growing season, although trees may be abundant on sites flooded for up to about 20% of the growing season. American hornbeam occurs less commonly in upland hardwood forests and may range from 300-900 meters elevation in the Appalachian and Adirondack Mountains. In the northeastern US, it may be an early migrant and form pure stands in moist old fields; it may be a minor seral component of sapling-size tree-shrub communities along the mid-Atlantic coast. Flowering: March-May; fruiting: August-October.

Acknowledgement

USDA, NRCS. 2008. The PLANTS Database (http://plants.usda.gov, 21 October 2008). National Plant Data Center, Baton Rouge, LA 70874-4490 USA.