The genus Carya is divided into three sections: Sinocarya, Apocarya and Carya. Rhamphocarya, considered by Manning (1978) as a monotypic section of Carya, is now placed in the genus Annamocarya. Detailed comparisons between that genus and North American sections are provided by Manning and Hjelmqvist (1951) and have recently been re-evaluated by Lu, et al. (1999). The newest section, Sinocarya, was proposed by Cheng and R. H. Chang (in Chang & Lu (1979). The section is characterized by species which lack terminal bud scales and includes only four Asian members of Apocarya (excluding C. poilanei).
Section Apocarya contains the "pecan hickories", while section Carya contains the "true hickories". The best method for distinguishing between the two sections is by comparing terminal buds; pecan hickories have (0)4 to 6 valvate bud scales that touch at the edges, but do not overlap; true hickories have 6 to 12 overlapping or imbricate terminal bud scales. It is interesting to note that the increasing development of bud scales is an adaptation to cold climates.
Other features, such as the number of leaflets per leaf and the presence of wings on the sutures of the husks, are helpful, but not as reliable. Pecan hickories tend to have greater numbers of leaflets than true hickories (5 to 13 in Apocarya vs 5 to 9 in Carya). Pecan hickories tend to have more pronounced wings on the sutures of the husk than do true hickories. If nuts are cut in cross section, those in section Carya do not have lacunae in the walls or internal ridges of the nut, and all have secondary septa, making the nuts 4 celled at the base. Species in section Apocarya have prominent lacunae and may have secondary septa (as in C. cordiformis) or lack them (as in pecan). . The Asian hickories lack lacunae. All species in Apocarya are diploids (n=16) while Section Carya includes both diploids and tetraploids (n=32).
LJ Grauke , Research Horticulturist & Curator
USDA-ARS Pecan Genetics
10200 FM 50
Somerville, TX 77879
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