Reproductive consequences of interactions between clonal growth and sexual reproduction in Nymphoides peltata: a distylous aquatic plant.

Distyly is a sexual polymorphism in which plant populations contain two floral morphs differing in morphology and physiology. The dimorphism serves to promote animal-mediated cross-pollination between the floral morphs. Clonal propagation can interfere with the functioning of distyly by compromising intermorph pollinations, resulting in reduced fertility. Here, we investigate the relations between clonal growth and sexual reproduction in the aquatic macrophyte Nymphoides peltata (Menyanthaceae). Surveys of morph representation in 30 populations from five regions of China revealed that most populations exhibited strongly biased morph ratios and 30% contained a single floral morph. Experimental pollinations indicate that N. peltata possesses a strong dimorphic incompatibility system preventing self and intramorph fertilizations. An experiment involving the manipulation of morph ratios in an experimental population and an investigation in a natural population with strong morph substructure both provided evidence that compatible pollen dilution limits fertility. Despite constraints on the functioning of distyly in N. peltata we found no evidence for evolutionary changes to the heterostylous syndrome, as reported in Nymphoides, including populations of N. peltata in other parts of its geographical range.