ABSTRACT
Hermaphroditic plant species present stylar polymorphisms across genera and families of flowering plants. Heterostyly and stigma-height dimorphism are commonly found in plant species with individual plants producing a single flower morph. It is often associated with actinomorphic flowers with deeply seated nectar. Enantiostyly is usually found in plant species associated with zygomorphy, nectarless non-tubular flowers, poricidal anthers, and even heteranthery. Inversostyly is reported only in Hemimeris racemosa, which offers oil as a floral reward for specialized oil-collecting bees. Resupinate dimorphy is reported in Orchidaceae and certain genera of different families of Lamiales. These species produce nectariferous resupinate flowers, which are adapted for nototribic pollination, and nectariferous non-resupinate flowers, which are adapted for sternotribic pollination. Flexistyly is reported in certain nectariferous genera of Zingiberaceae. Diplostigmaty is a novel expression of flexible mixed-mating system in Sebaea genus of Gentianaceae. In each flower, the pistil possesses functional apical stigma evolved for promoting out-crossing and basal stigma evolved for reproductive assurance through autonomous self-pollination. The stylar polymorphisms evolved variously in different hermaphroditic species that ensure adaptability to insect pollination and reproductive success by promoting cross-pollination and reducing self-pollination are discussed in this chapter.
