Stamen movements in flowers of Opuntia ( Cactaceae ) favour oligolectic pollinators

摘要: Opuntia brunneogemmia andO. viridirubra occur sympatrically in the Serra do Sudeste, Rio Grande Sul, Brazil. Their flowers have 450–600 thigmonastic stamens and provide large amounts of pollen nectar for bees. Bees 41 species were registered at ofO. 30 viridirubra. Females three oligolectic are only effective pollinators:Ptilothrix fructifera (Anthophoridae),Lithurgus rufiventris (Megachilidae), andCephalocolletes rugata (Colletidae). During their visits inOpuntia-flowers, bees touch filaments stimulate movement to centre flower. At end this movement, anthers densely packed around style. As a consequence is presented an easily accessible upper layer various, nearly inaccessible lower layers. The layers contain about 80% reward. Only females pollinators exploit from reach furrow. Therefore, through stamen movements,Opuntia hide most flower visitors but favour effectively pollinating,