Bitternut Hickory is a medium to large native deciduous tree growing 60 to 80 feet high and over 2 feet in diameter, with a broad and rounded crown with ascending branches. The crown will be more narrowed in close quarters.
The bark is thin, silver gray, smooth and tight to the tree initially, turning gray later and shallowly furrowed into narrow forking scaly ridges.
Twigs are slender, smooth, with 3-lobed leaf scars. New growth is greenish with scattered lenticels. Buds are slightly flattened and bright yellow or sulfur-yellow in color with a powdery coating. The scales of the bud butt together, rather than overlap (are 'valvate'). Lateral buds are protected by a pair of very small bracts.
Leaves are alternate and pinnately compound, 6 to 10 inches long with 7 to 9 leaflets (some 7 to 11), that are stalkless, lance-shaped and finely saw-toothed on the margins. Those closest to the terminal leaflet are larger in size. The upper surface varies from yellow-green to dark green while the underside is lighter with hair on the central stem of the leaf. They turn yellow in the Autumn.
Flowers: The tree is monoecious, that is with separate male and female flowers. Male flowers are yellow-green in slender drooping catkins, 3 to 4 inches long, 3 from one stalk from the previous years twig or at the base of this years twig. The tiny male flowers have a 3-lobe calyx and several hairy stamens. Female flowers are about 1/8 inch long, appearing on a short terminal spike at the tips of this years twigs. They have a 4-ridged ovary and a pair of styles. Flowers cross pollinate by wind.
Seed: Fertile female flowers produce a 3/4 to 1-1/4 inch, nearly round or slightly flattened nut, covered by a thin husk with small yellow scales and with a sharp-pointed tip. Above the middle of the husk are 4 small wings, along which the husk splits. Fruit matures in the Autumn and drops from the tree the same year. The nut inside a dusty yellow color, bitter and inedible and most wildlife avoid them. Trees must be around 30 years of age to produce a good crop.
Habitat: Bitternut Hickory has a root system with a taproot and spreading laterals. It sprouts easily from laterals and stumps. It grows in mixed woodlands with fertile somewhat moist soil, but is not very shade tolerant.
Names: The genus name Carya is an old name for walnut in which family this tree resides. The species, cordiformis, means 'heart-shaped' and refers to the somewhat heart-shape of the nut. The author names for the plant classification start with ‘Wangenh.’ who was Friedrich Adam Julius von Wangenheim (1749-1800), German botanist who specialized in forestry and while in the United States studied trees and shrubs of the colonies while he was a Hessian cavalry commander in British service, taking part in several Revolutionary War battles. His work on this species was furthered by ‘K. Koch’ - Karl Heinrich Emil Koch (1809-1879), German botanist, Professor of Botany, first professional horticultural officer in Germany, and a plant collector in and near Asia Minor.
Chain of names: While the common name of Bitternut Hickory has been in continuous use, the tree has had a series of botanical names applied over the last three centuries. As it is in the Walnut Family, it was named Juglans ovata in 1768; Juglans alba Linnaeus, var. minima in 1785 by Marshall; Juglans cordiformis in 1787 by Wangenheim; Juglans amara in 1810 by Michaux; Carya amara in 1859 by Nuttall; Hicoria minima in 1888 by the Torrey Botanical Club; Hicoria cordiformis in 1908 by Britton and Shafer; and finally Carya cordiformis of 1869 by K. Koch is currently the accepted name.
Comparisons: The nearest comparison is the Shagbark Hickory, C. ovata, which has seeds with much more stout husks and bark that looks like it is shedding off the tree.
Above: Bitternut Hickory has a broad crown with ascending branches. Older bark is gray and shallowly furrowed into narrow forking scaly ridges. Twigs (3rd photo) have a 3-lobed leaf scar. The buds are bright yellow or sulfur-yellow in color with a powdery coating. Note how scales of terminal bud on the spring twig above butt together rather than overlap.
Below: 1st & 2nd photos - The compound leaf has 7 to 9 leaflets with the 2 next to the terminal leaflet being larger in size. Margins have a fine sawtooth. 3rd photo - The new catkins of the male flowers at the base of new growth.
Below: 1st photo - A typical leaf showing upper side color. 2nd photo - The underside of the leaf is paler color and has fine white hair on the ribs.
Below: 1st photo - The male catkins at the pollination stage. 2nd photo - fruit forming.
Below: The fruit of Bitternut Hickory is nearly round or slightly flattened nut, covered by a thin husk with small yellow scales and with a sharp-pointed tip. Above the middle of the husk are 4 small wings (ridges), along which the husk splits. The nut inside a dusty yellow color.
Notes: Bitternut Hickory is not indigenous to the Garden. Eloise Butler planted the first specimens in April 1913 with plants she had shipped in from Kelsey's Nursery in North Carolina. At that time the scientific name in use by her was Hicoria minima. She planted again in 1915, '16' and '24. Martha Crone also planted the tree in 1935 and 1936. Garden Curator Susan Wilkins added additional plants in 2008 and 2010. The tree is found in North America in the eastern half, from Minnesota to Texas on the west then east to the coast in the US and in Canada it is known in Ontario, Quebec and P E Island. Within Minnesota, it is found in less than 1/3 of the counties, all on the eastern side of the state, but it is much more prevalent than the Shagbark Hickory, C. ovata. C. cordiformis and C. ovata are the only two species of Carya native to Minnesota.
Uses: The wood of Bitternut Hickory is strong and hard, but heavy. On the Janka Hardness Scale hickory rates 1820 compared to Red Oak at 1290 or Hard Maple at 1450. Hardness is useful for small wooden objects like tool handles, dowels and for furniture. It also makes good charcoal and for smoking food (i.e. "hickory smoked").
Older Commentary: In his 1817-1819 3 volume North American Sylva, Francois Michaux (Ref.# 26b) wrote: I have measured trees which were 10 or 12 feet in circumference, and 70 or 80- feet high. (in OHIO). Of all the Hickories, the vegetation of this species is the latest I have uniformly observed, that its leaves unfold a fortnight after the others. In parts of Pennsylvania where this tree is multiplied, an oil is extracted from the nuts, which is used in burning in lamps and other inferior purposes…. Hickory timber [all types] is employed in no part of the United States in the building of houses, because, as has been before observed, it is too heavy, and soon becomes worm eaten. …it [Bitternut] resembles the other Hickories, and its wood possesses, though in an inferior degree, the weight, strength, tenacity and elasticity which so plainly distinguish them.
References: Plant characteristics are generally from sources 1A, 32, W2, W3, W7 & W8 plus others as specifically applied. Distribution principally from W1, W2 and 28C. Planting history generally from 1, 4 & 4a. Other sources by specific reference. See Reference List for details.
Identification booklet for most of the flowering forbs and small flowering shrubs of the Eloise Butler Wildflower Garden. Details Here.
Friends of the Wild Flower Garden, Inc. Text and photos are by G. D. Bebeau unless otherwise credited. "www.friendsofthewildflowergarden.org"