Pollination biology of Humiria balsamifera var. floribunda (Humiriaceae) on the coast of Maranhão, Brazil

Research into pollination ecology provides information on plant reproduction, interactions with pollinators and biodiversity conservation. Humiria balsamifera occurs only in South America and presents an infraspecific complex with 10 varieties recorded in the most recent taxonomic revision. The current study aimed to evaluate the phenological events of flowering and fruiting, floral biology, floral visitors, and the reproductive system of H. balsamifera var. floribunda, in a restinga area in Maranhão, Brazil, in the year 2017. The production of floral buds, flowers, and fruits in 20 individuals was evaluated by the Fournier method. The phenophases presented no correlations with temperature, humidity, and rainfall, except for the production of immature fruits, which increased in the drier months. The species presents a large number of flowers in cymose-paniculate inflorescences, which open at 7:00 am and last less than a day. Nectar is the main resource exploited by the floral visitors. In all, 1393 floral visitors were observed distributed in 49 morphospecies, 94.75% of which were bees and wasps, including Melipona subnitida, Apis mellifera, Xylocopa cearensis, Melipona fasciculata, Polybia sericea and Megalopta amoena as the most abundant. Visitor activity occurred in all daytime hours and months of the year, but the abundance of specimens increased with flowering and reduced rainfall. Reproductive system tests indicated that H. balsamifera var. floribunda presents facultative xenogamy, requiring pollen vectors for its reproductive success. This work reinforces data on other varieties of the species and demonstrates the environmental importance of the plant to sustain fauna.