The hickories are members of the walnut family, Juglandaceae. They constitute the genus Carya, which is a genus in the subtribe Caryinae of the tribe Juglandeae (Manos and Stone, 2001). Authorities disagree on the number of species recognized within the genus, with much of the disagreement centering on inherent ambiguities in the concept of "species". The taxa presented here fulfill the following criteria of species status; 1) they are morphologically distinct (although at times only obscurely); 2) they each have ecological adaptations which reduce competition with related, neighboring species; and 3) they have some level of reproductive isolation which limits gene exchange with other species (see Grant 1957). Grant (1980) has suggested that the ultimate criterion of species status is reproductive isolation. The genus Carya is characterized by numerous interspecific hybrids, some of which (e.g. C. X lecontei Little) are commonly encountered when the two parent populations overlap. Detailed evaluation of the level of reproductive isolation has not been conducted. After more critical evaluation, some of these taxa may be placed at other taxonomic levels.

LJ Grauke , Research Horticulturist & Curator
USDA-ARS Pecan Genetics
10200 FM 50
Somerville, TX 77879
fax: 979-272-1401

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