Comparison of common cytotypes of Andropogon gerardii (Andropogoneae, Poaceae)

Many plant species contain populations with more than one polyploid cytotyp e, but little is known of the mechanisms maintaining several cytotypes in a population. Andropagon gerardii cytotypes were compared to evaluate differ ent models of autopolyploid cytotype coexistence. The enneaploid (90 chromo some, 9x) cytotype was found to be larger and taller than the hexaploid (60 chromosome, 6x) cytotype. Seed production is significantly more efficient in hexaploids, but seed production per area was not significantly different . The two cytotypes are not exomorphologically separable in the held becaus e of great plasticity in response to environmental variation and wide varia tion within each cytotype. These data suggest cytotypic variation is mainta ined by natural selection.