ABSTRACT
Enantiostyly is a floral polymorphism that evolved independently in 11 Angiosperm families and has broad distribution, but most species are in the tribe Cassiinae (Fabaceae). Floral morphs exhibit reciprocal arrangement of sexual organs in a horizontal plan; species have right (style deflected to the right) and left flowers (style deflected to the left). Considering the reciprocal positioning of stigma and anthers in the flowers, right flowers deposit pollen at the left and capture pollen at the right portion of pollinators' bodies, whereas left flowers perform the inverse. Enantiostylous species may be monomorphic (both floral morphs in the same individual, and most commonly recorded in Angiosperms) and dimorphic (only one morph per individual). Geitonogamy and autogamy rates are considered as the main selective pressures in the evolution of monomorphic to dimorphic type. Considering that self- and intramorph-incompatibility are rare, enantiostylous species rely on flower morphological characters to maximize the chances of intermorph crosses. Similar proportion of floral morphs (also called isoplethy) is commonly recorded. Some studies reported deviations from the enantiostylousmorpho-functional pattern, such as the presence of functionally central flowers, aggregate enantiostyly, and functional dimorphism in monomorphic species. Several aspects on enantiostyly deserve attention in future studies, such as the genetics driving enantiostylousmorpho-functional patterns, the evolutionary maintenance of monomorphic enantiostyly, establishment of a measurement pattern for the reciprocity of floral parts, and variations found in typical and atypically enantiosylous taxa.
