| Sex expression was found to be basically a genetically determined character. The sex expression of male and female plants was always consistent, however, environmental influences may affect the sex expression of monoecious plants. In general, the sex form ratio and inflorescence sex ratio of male to female sex forms was not different from a 1:1 ratio and was not variable between natural populations. The frequency of monoecious sex forms was variable between natural populations and was closely related to the area of distribution. Inflorescence sex ratio of monoecious individuals was also variable between natural populations but no pattern was observed for these variations. The male sex form allocated more biomass to vegetative plant parts and less to sexual reproduction and roots than the female sex form. The sexual reproductive biomass allocation by female and monoecious sex forms was more responsive to environment than that of the male sex form and thus, represents a potential for differential niche adaptation between the sex forms of this species. In natural populations, sex forms are expected to segregate into a patchwork of single sex forms rather than exist as swards of mixed sex forms. Within the shortgrass prairie, natural populations were different in morphology. Leaf pubescence was closely related to the area of distribution and male and female inflorescences were differentially affected by herbivore grazing pressure. Sex expression has a low heritability and has large dominance and/or environmental variance components. The frequency of monoecious sex form is a genetic property of natural populations and is predicted to respond more to selection pressure than the male to female sex form ratio because of the larger amount of additive genetic variance controlling this character. |
