Heterostyly
Heterostyly is a unique form of polymorphism and herkogamy in flowers. In a
heterostylous species, two or three morphological types of flowers, termed
morphs, exist in the population. On each individual plant, all flowers share the same morph. The flower morphs differ in the lengths of the pistil and stamens, and these traits are not continuous. The morph phenotype is genetically linked to genes responsible for a unique system of self-incompatibility, termed
heteromorphic self-incompatibility, that is, the pollen from a flower on one morph cannot fertilize another flower of the same morph. Heterostylous plants having two flower morphs are termed
distylous. In one morph the stamens are short and the pistils are long; in the second morph the stamens are long and the pistils are short; the length of the pistil in one morph equals the length of the stamens in the second morph, and vice versa. Examples of distylous plants are the primrose and many other
Primula species, flax and other
Linum species, some
Lythrum species, and many species of
Cryptantha.