Abstract
Knowledge of reproductive biology and pollination of Neotropical tree species has been increasing in recent decades. However, this is still incipient in the Atlantic Forest, and many questions remain, for instance, about the prevalence of self-incompatibility. We studied the floral biology, breeding system and floral visitors of Senna multijuga in order to verify the occurrence of self-incompatibility and determine its pollinators. This species bears the typical floral traits of the genus, such as asymmetry, enantiostily, heteranthery and poricid anthers. Anthesis is diurnal and pollen viability did not differ among the morphs of anthers. Pollinators were bees of the genera Bombus, Epicharis, Centris and Xylocopa and smaller bees acted as pollen thieves. Sexual reproduction of Senna multijuga depends on the transfer of pollen by pollinators, as no fruit was formed by either apomixis or self-pollination. The latter result may be due to inbreeding depression or by a mechanism of late-acting self-incompatibility, as we observed after self-pollination both penetration of pollen tubes in the ovules and uniform abortion of pistils. Differences on fertility after manual crossings and under natural conditions indicate that female fitness is affected by pollen limitation, as well as by the availability of resources.
Key words:
inbreeding depression; late-acting self-incompatibility; pollen flower; pollination