Maternal and paternal success among flower morphs in tristylous Lythrum salicaria

Morph-specific patterns of success as maternal and paternal parents were st udied in a factorial pollination experiment with long-, mid- and short-flor al morphs in tristylous Lythrum salicaria L. 'Legitimate' pollinations (inv olving stamens and stigma of similar heights) produced greater fruit and se ed set than 'illegitimate' intermorph pollinations (involving stamens and s tigma of dissimilar heights between different morphs), 'illegitimate' intra morph pollinations (between two individuals of the same floral morph) and s elf-pollinations (pollination involving stamens and stigma of the same flow er). The mean rate of germination of seeds produced by legitimate and illeg itimate crosses was 81.4% and 72.7%, respectively. The three flower morphs differed significantly in their ability to act as maternal parent but did n ot differ paternally, following legitimate pollinations. Significantly grea ter legitimate seed set was recorded for the long morph compared to the sho rt morph, when these individuals acted as maternal parents. Incompatibility (as measured by seed set) was weakest in the mid-morph individuals and str ongest in short-morph individuals. Following self-pollination events, polle n from the mid- and long whorls of stamens within a flower produced seeds i n the long and mid-morphs, respectively. This suggests that the self-compat ibility differs between the two whorls of stamens, and is greater in the lo nger stamens than in the shorter stamens in the long and mid-morphs. (C) 19 99 Elsevier Science B.V. All rights reserved.