heteromorphism

Heteromorphism is the occurrence within a single species of two or more discrete morphological forms. The term derives from Greek heteros “other” and morphe “form,” and it is used across biology to describe qualitative, rather than quantitative, differences among individuals. Heteromorphism can arise from genetic polymorphism, phenotypic plasticity, or developmental polyphenism; in some cases, morphs are seasonally or environmentally induced.

In plants, heteromorphism covers phenomena such as heterophylly—the presence of different leaf forms on the same plant or in different organs—and heterostyly, a floral polymorphism that reduces self-fertilization by having distinct stigma and anther positions in different morphs, found in several genera (e.g., Primula). In animals, heteromorphism commonly refers to cases where members of the same species display distinct adult forms, such as winged versus wingless adults in aphids or other insects, or different body sizes or castes in social insects.

The functional significance of heteromorphism varies by system. It can enhance dispersal, promote outcrossing, partition ecological niches, or respond to environmental heterogeneity. Heteromorphism is related to broader concepts of polymorphism and polyphenism, which describe phenotypic variation within populations, either genetically fixed or environmentally induced.