EVOLUTIONARY IMPLICATIONS OF MEIOTIC CHROMOSOME BEHAVIOR, REPRODUCTIVE-BIOLOGY, AND HYBRIDIZATION IN 6X AND 9X CYTOTYPES OF ANDROPOGON-GERARDII (POACEAE)

Andropogon gerardii, big bluestem, has 60 and 90 chromosome cytotypes. Meiosis in the hexaploid was shown to be regular, although some secon dary associations of bivalents form. Meiosis in the enneaploid (2n = 9 x = 90) is irregular, leading to most gametes having unbalanced chromo some complements. Both cytotypes show considerable self-incompatibilit y. Cytotypes crossed freely, forming a variety of fertile euploids and aneuploids. Indistinguishable exomorphology, intermixing in natural p opulations, and compatibility suggest that A. gerardii is best underst ood as a cytotypically complex single species.