The Development of Heterostyly

Abstract

Heterostyly is a genetic polymorphism in which the two (distyly) or three (tristyly) mating types in a population differ in floral morphology. The principal feature that distinguishes the floral morphs is that they differ in stigma and anther heights. The sex organs are reciprocally positioned with anthers in flowers of one morph at the same level as stigmas in flowers of the other morph(s). This structural difference is usually accompanied by a physiological self- and intramorph incompatibility that limits mating to crosses between organs at the same level. In this chapter we describe the diversity of organization in heterostylous flowers, consider the developmental bases for this diversity, and examine the genetic and environmental components of phenotypic variation in heterostylous breeding systems. We review the developmental implications of models for the genetic control and evolution of heterostyly and conclude with recommendations for future research.