Abstract: Enantiostyly, deflection of style to left or to right side of floral axis, is a kind of style polymorphism. Based on organization of left- and right-styled flowers present on individual plants, enantiostyly can be expressed as two quite distinct forms: monomorphic and dimorphic enantiostyly. In monomorphic enantiostyly, individual plants produce both floral forms, either mixed within an inflorescence or segregated between left- and right-styled inflorescences, and this condition is not a genetic polymorphism. In dimorphic enantiostyly, plants are exclusively left- and right-styled, and this condition is a genetic polymorphism. Based on patterns of arrangement of style and stamens in individual flowers, enantiostyly can be expressed as reciprocal and nonreciprocal enantiostyly. Reciprocal enantiostyly is commonly associated with the reciprocal deflection of a pollinating anther, but in nonreciprocal enantiostyly there are no pollinating anther deflections. Enantiostyly has been reported in 11 families of angiosperm. It is generally considered to play an important role in (1) protecting the functional pistil and stamens, (2) insuring reproduction by selfing, and (3) increasing male fitness and outcrossing rates by reducing sexual interference between female and male function. Enantiostyly has been hotly-debated in plant reproductive biology. The purpose of this paper is to review and analyze recent advances in enantiostyly research, with emphases on 1) types of enantiostyly and morphological differentiation and floral characteristics of mirror-image flowers; 2) taxonomy, genetics and evolution of angiosperms that exhibit enantiostyly; and 3) the evolutionary biology of mating patterns and pollinating characteristics associated with enantiostyly. Finally, prospects for further research in this area are discussed. Our review provides a database for further study of the evolutionary biology of enantiostylous species and points out the significance of enantiostyly in the evolution of breeding systems of plants.

Key words: angiosperms, breeding system, enantiostyly, evolution