heterostyly A polymorphism among angiosperm flowers that ensures cross-fertilization through pollination by visiting insects. Flowers have anthers and styles of different lengths; usually the anthers of one morph are at the same level as the stigmas of another. A well-known example is the pin-eyed (long style) and thrum-eyed (short style) forms of Primula vulgaris (primrose).

heterostyly The condition of flowering plants in which flowers of the same species have styles of different lengths, so that the stigma is positioned below the anthers in some flowers and above them in others. This ensures that pollinating insects are more likely to transfer pollen from the anther of one flower to the stigma of another, thus promoting cross-pollination. Species showing heterostyly include the primrose (see illustration).

heterostyly A polymorphism that occurs in some species of flowering plants, which produce flowers with anthers and styles of different lengths. This ensures cross-pollination (e.g. the pin-eyed (long style) and thrum-eyed (short style) forms of the primrose, Primula vulgaris).