Floral Variation and Breeding System in Distylous and Homostylous Species of Clonal Aquatic 'Nymphoides' (Menyanthaceae)

Abstract

This study focuses on floral variation and the breeding system of two species of the clonal aquatic 'Nymphoides' (Menyanthaceae), in particular, the phenomena of distyly, loss of sex and homostyly. Distyly is a floral design that promotes efficient pollen transfer while reducing self-interference and self-pollination. Populations of distylous species contain two floral morphs that differ in the reciprocal positioning of the sex organs; i.e. reciprocal herkogamy. Distylous species usually possess a dimorphic incompatibility system in which only pollination between flowers of different morphs produce seed. There are, however, atypical features of distyly, which provide excellent examples to study the maintenance or evolutionary transition of this breeding system. 'Nymphoides montana' is a perennial clonal aquatic species, native to Australia, found in shallow water on the edges of wetlands. Selective factors that maintain distyly were sought by examining floral morphologies, compatibility relationships, morph frequencies and reproductive success in three 'N. montana' populations.