MORPH-BIASED MALE-STERILITY IN THE TROPICAL DISTYLOUS SHRUB ERYTHROXYLUM HAVANENSE (ERYTHROXYLACEAE)

This study explores whether ecological factors, such as pollinators an d pollen flow, or variation in pollen and ovule development account fo r the observed differences (approximately twofold) in the reproductive output of pin and thrum individuals of Erythroxylum havanense. The im portance of ecological factors was assessed by means of comparison of the identity of pollinators and the rates of flower visitation, and by performing controlled hand pollinations and measurements of fruit set . In addition, we described the pollen and ovule development of thrum and pin individuals. Our results indicate that pollinators of E. havan ense do not distinguish between floral morphs. The differences in frui t set between pin and thrum plants held even after hand pollination an d, therefore, the observed differences in reproductive output between floral morphs of E. havanense cannot be explained in terms of asymmetr ical pollen flow. There were no differences in the pattern of gynoeciu m development between the pin and thrum morphs, however androecium dev elopment showed marked differences between the morphs, and there was a resemblance between the developmental pathways leading to male steril ity of the thrum morph of E. havanense with that of species with cytop lasmic male sterility (CMS).