CLONAL POPULATION-STRUCTURE AND GENETIC-VARIATION IN SAND-SHINNERY OAK, QUERCUS-HAVARDII (FAGACEAE)

We investigated clonal population structure and genetic Variation in Q uercus havardii (sand-shinnery oak), a deciduous rhizomatous shrub tha t dominates vegetation by forming uninterrupted expanses of ground cov er over sandy deposits on the plains of western Texas, western Oklahom a, and eastern New Mexico. Isozyme electrophoresis (15 loci coding 11 enzymes) was used to recognize and map clones arrayed in a 2000-m tran sect (50-m sample intervals) and a 200 x 190 m grid (10-m sample inter vals). Ninety-four clones were discovered, 38 in the transect and 56 i n the grid, resulting in an estimated density of similar to 15 clones per hectare. Clones Varied greatly in size (similar to 100-7000 m(2)), shape, and degree of fragmentation. The larger clones possessed massi ve interiors free of intergrowth by other clones, while the smaller cl ones varied in degree of intergrowth. The population maintained substa ntial levels of genetic variation (P = 60%, A = 2.5, H-exp = 0.289) co mparable to values obtained for other Quercus spp. and for other long- lived perennials. The population was outcrossing as evidenced by confo rmance of most loci to Hardy-Weinberg expected genotype proportions, a lthough exceptions indicated a limited degree of population substructu ring. These data indicate that despite apparent reproduction primarily through vegetative means, Q. havardii possesses conventional attribut es of a sexual population.