The breeding biology of Amaioua guianensis was studied in a forest area at Parque do Sabiá in Uberlândia, MG, Brazil, between September 2003 and April 2005. Phenology, breeding system, flower morphology, pollinator and disperser's assemblages, and sexual structure of the reproductive individuals were investigated. Amaioua guianensis is a woody dioecious species common in Brazilian forest areas. Flowers are hexamerous, tubular, whitish and odoriferous, pollinated by relatively specialized vectors as large bees and hawkmoths. Pistilate flowers produced nectar earlier and in larger amounts than the staminate ones. Staminate flowers were produced in larger numbers per inflorescence and were significantly larger than the pistilate ones. Flowers were presented in terminal inflorescences, composite umbels in the staminate and simple ones in pistilate individuals. Both male and female flowers produced non-functional sexual structures of the opposite morph, but the style of male flowers act as a pseudo-stamen, a secondary pollen presentation mechanism which is common in the tribe Gardenieae but had not been described previously to the species. Sexual ratio was significantly male biased and gender was distributed contagiously in the area, probably due in both cases to vegetative multiplication and disturbance. Natural pollination was as high as 98.6% and fruit set was 75.7%. Apomictic fruit production was very low (3.4%). Fruits were dispersed by birds. Floral morphology and relatively specialized pollinator's fauna rendered efficient pollination service and fruit production in the species even in the relatively disturbed study area.
Amaioua; dioecy; pollination; Rubiaceae; secondary pollen presentation
