Allozyme variation and genetic relationships among species in the Carex willdenowii complex (Cyperaceae)

A taxonomic study by Naczi, Reznicek, and Ford (American Journal of Botany, 85, 434-447, 1998) has determined that three species (Carex willdenowii, C. basiantha, and C. superata) can be recognized within the C. willdenowii complex. To determine the amount of genetic divergence within and between these species, allozyme analyses were conducted on 14 populations distributed from Pennsylvania to eastern Texas. Seventeen loci were surveyed, 13 of which were polymorphic, with all populations being polymorphic at one or more loci. Interspecific genetic identities ranged from 0.560 (C. willdenowii and C. basiantha) to 0.807 (C. basiantha and C. superata). Alleles for the isozymes Aat-1, Dia-1, Idh-2, Mdh-2, Per-1, Pgm-1, and Pgm-2 served to distinguish C. willdenowii from C. basiantha and C. superata. Carex basiantha and C. superata were recognized by alleles of Mdh-2, Pgm-1, and Tpi-2. The genetic identities of populations within species were high and exceeded 0.957. A caespitose growth habit and perigynia in close proximity to the staminate flowers suggest adaptations for selfing and therefore low levels of heterozygosity. Paradoxically, the values for expected heterozygosities (Hexp) were always lower than those obtained by direct count (Hobs): F values were highly negative, indicating heterozygous excess. Disassortative mating and selection are discussed as possible mechanisms for maintaining heterozygous excess within populations.