The reproductive biology of two species of Diplusodon Pohl (Lythraceae) from Serra do Cipo, southeastern Brazil

The reproductive biology of two shrub species of Diplusodon (Lythraceae), D . hirsutus and D. orbicularis, was studied. Their distribution is restricte d, mainly associated with "campos rupestres", a montane biome in SE Brazil. Both species proved to be self-compatible but because of herkogamy they ar e greatly dependent on visitors to effect pollination. The main pollinators are medium-sized bees. In experiments where pollinators were excluded or d iscouraged the percentage of abscised fruits was total or extremely high; m ost of these fruits dropped within the first two weeks after pollination in D. orbicularis and three weeks in D. hirsutus. The percentage of surviving fruits from control or manual pollination was higher in D. orbicularis (co . 70%) than in D. hirsutus (co. 50%). Seed set was very variable, with slig htly lower means in D. hirsutus. Within each species the mean seed set was similar in self-, cross-pollinated fruits, and controls. In both species, t he similarity between control and manual pollination fruit survival curves suggests that factors other than pollen limitation are the cause of abortio n in the study area. The high rate of abscission, which was also observed i n unmanipulated fruits, was attributed to resource limitation. In D. hirsut us this was caused by drought during seed development. In D. orbicularis it was enhanced by nutrient drain by shoot-galling flies. The lack of selecti ve abortion of either selfed fruits or fruits with a small number of seeds may be a useful mechanism to overcome this detrimental effect which is felt later during fruit development.