MIRROR-IMAGE FLOWERS AND THEIR EFFECT ON OUTCROSSING RATE IN CHAMAECRISTA-FASCICULATA (LEGUMINOSAE)

The influence of enantiostyly (reciprocal segregation of anthers and s tigmas to different sides of the flower) on outcrossing rate was exami ned in Chamaecrista fasciculata (Leguminosae). I hypothesized that ena ntiostyly has not evolved to increase the female component of outcross ing and actually acts to increase the selfing rate through geitonogamy . To quantify the role of enantiostyly to outcrossing, plants of known isozyme genotype were manipulated to be either completely left- or ri ght-styled (nonenantiostylous) or to have equal numbers of left- and r ight-styled flowers (enantiostylous). Flower number was varied to quan tify any interaction between floral display size and enantiostyly on o utcrossing rate. These ''target'' plants were surrounded by unmanipula ted plants homozygous for the alternative allele. Outcrossing rates of the target plants were determined by scoring the presence or absence of heterozygotes. The contribution of enantiostyly to geitonogamy may be reduced if pollinators discriminate among the floral types. Thus, o bservations of pollinator movement between flowers on the same plant w ere made to determine if pollinators discriminate between the floral t ypes. Although pollinators moved randomly between flower types, outcro ssing rate was only marginally effected by the presence of enantiostyl y. Enantiostylous plants outcrossed at a slightly lower rate than none nantiostylous plants only when the opportunity for geitonogamy was gre at. These results suggest that the contribution of enantiostyly to sel fing is minimal.