In a mixed population ofAndropogon glomeratus var.pumilus andA. longiberbis in Lake County, Florida, there were six individuals morphologically intermediate between and less fertile than these two taxa. In a discriminant analysis using two characters, spikelet length and raceme sheath width, the putative hybrid plants are significantly different from both parents (P<0.01). Reproductive isolation of these taxa in other mixed populations comes, at least in part, from a combination of nonsynchronous flowering and cleistogamy.