Carya cordiformis

C. cordiformis (Wangenh.) K. Koch. Bitternut Hickory

Bitternut hickory is possibly the most widely and uniformly distributed hickory, being found as far north as southern Quebec, Canada and as far south as the Gulf Coast of Louisiana. It is found throughout the Eastern United States from New Hampshire south to Florida and west to Minnesota and eastern Texas (distribution map) . The species occurs on a wide range of sites, from dry upland sites in the southwestern part of its range to low wet woods in Louisiana (Fowells 1965, Grauke et al 1987). Bitternut is a major component of the White Oak-Red Oak-Hickory forest in the northern U.S. and of the Swamp Chestnut Oak-Cherrybark Oak forest in the south (Fowells 1965).

C. cordiformis is easily recognized by its
distinctive buds, leaves, nuts and bark. Terminal buds have sulphur yellow, leaf-like bud scales. Leaves are distinctive by the combination of their general symmetry and the presence of large, clear, plate-like scales on the lower leaflet surface, near the basal margin of the leaflet. The fruit is a slightly flattened sphere with a prominent point at the apex, making the nut almost heart-shaped. The name "cordiformis" means "heart-shaped". Husks are thin and have prominent wings on the sutures from the apex to the middle of the nut. Husks dehisce to the middle, but the nut often drops in the husk. Nuts have very thin shells marked by shallow grooves. Cross sections of the nuts reveal prominent lacunae and a well developed secondary septum which extends to the middle of the nut. Kernels are crinkled and bitter. The bark of mature trees is tight, smooth and very light gray, a feature shared by the Mexican endemic C. palmeri.

The wood of C. cordiformis is inferior to that of the true hickories, leading Boisen and Newlin (1910) to recommend that it not only should not be planted, but should be removed from existing stands in favor of shagbark, shellbark, pignut and mockernut.

C. cordiformis has received little horticultural attention, due to its bitter kernel. There are however, two named cultivars of bitternut, 'Halesite' and
'Hatch'. Willard Bixby entered the nuts of 'Halesite' in the Northern Nut Grower's 1918 nut contest and won the title of "thinnest shelled hickory". The 'Dennis' hickory is also C. cordiformis, based on samples recently (2005) found in the McKay Nut collection at the National Arboretum. When shell thickness was compared on 10 nuts from each of 5 trees from each of the 13 U.S. hickories, the thinnest shells were found on C. aquatica, while bitternut and pecan could not be distinguished (Ring, unpublished data).

Interspecific hybrids have been reported between C. cordiformis and pecan (C. X brownii). McDaniel (1968) speculated that interspecific hybridization between pecan and bitternut might have extended the northern range of pecan by contributing genes for early ripening of nuts. Named cultivars of that cross include 'Galloway', 'Mall', 'Nelson', 'Pleas', 'Pooshee', and 'Westbrook'(see Table 3). Hybrids typically have nuts which are somewhat flattened, have prominent apices, and are four-celled at the base due to the presence of a secondary septum as in C. cordiformis. Nuts may be astringent, as in 'Pleas', or "sweet-fruited" as in 'Galloway' (see Trelease 1896).

Interspecific hybrids have also been reported between C. cordiformis and C. ovata (C. X laneyi). Detailed description of this family of crosses is offered by Manning (1948). The following cultivars have been named; 'Beaver', 'Creager', 'De Acer', 'Fairbanks', 'Laney' (type tree), 'Peck', 'Roof', 'Stocking', 'Stratford', 'Terpenny', and 'Weschcke'.
'Brackett', wrongly attributed as a species of Carya glabra, is also C. X laneyi (see Thompson and Grauke, 1991, page 877). Samples of 'Brackett' were also found in the McKay Nut Collection (LJG, 2005).

C. X demareei is supposedly a hybrid between C. cordiformis and C. ovalis (see Palmer 1937). This hybrid is reported from the area near Crowley's Ridge in northeastern Arkansas.

LJ Grauke , Research Horticulturist & Curator
USDA-ARS Pecan Genetics
10200 FM 50
Somerville, TX 77879
fax: 979-272-1401
e-mail: ljg@tamu.edu

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