Maternal and paternal success among flower morphs in tristylous Lythrum salicaria

Abstract

Morph-specific patterns of success as maternal and paternal parents were studied in a factorial pollination experiment with long-, mid- and short-floral morphs in tristylous Lythrum salicaria L. `Legitimate' pollinations (involving stamens and stigma of similar heights) produced greater fruit and seed set than `illegitimate' intermorph pollinations (involving stamens and stigma of dissimilar heights between different morphs), `illegitimate' intramorph pollinations (between two individuals of the same floral morph) and self-pollinations (pollination involving stamens and stigma of the same flower). The mean rate of germination of seeds produced by legitimate and illegitimate crosses was 81.4% and 72.7%, respectively. The three flower morphs differed significantly in their ability to act as maternal parent but did not differ paternally, following legitimate pollinations. Significantly greater legitimate seed set was recorded for the long morph compared to the short morph, when these individuals acted as maternal parents. Incompatibility (as measured by seed set) was weakest in the mid-morph individuals and strongest in short-morph individuals. Following self-pollination events, pollen from the mid- and long whorls of stamens within a flower produced seeds in the long and mid-morphs, respectively. This suggests that the self-compatibility differs between the two whorls of stamens, and is greater in the longer stamens than in the shorter stamens in the long and mid-morphs.