Reproduction biology of Mimosa bimucronata: a ruderal species

摘要

Aiming to study the reproduction biology of Mimosa bimucronata, this work was developed in two municipalities, Botucatu and Cachoeira Paulista, São Paulo, in southeastern Brazil, between November 2003 and June 2005. The number of flowers per flower head, flower lifetime, anthesis events and other floral characteristics, such as flower size, color, nectar, scent, and osmophore location, were studied. Stigma receptivity and pollen viability were evaluated. The flowers were observed and documented in a scanning electron microscope, after receiving a proper treatment. Tests were performed to investigate the reproductive system, aiming to evaluate the reliance on pollinators. Floral visitors were observed directly in the field and their frequency, duration of visits and behavior on flowers were registered. M. bimucronata showed an annual flowering pattern. The pollen grains are united in polyades with eight cells, which are interpreted as an adaptation to minimize mixed pollen grain loads on the minute stigma. Fruit set was low in natural conditions and there was no occurrence of agamospermy or spontaneous self-pollination. The flower and inflorescence morphology allow access to several orders of visitors. Members of Hymenoptera, Diptera and Coleoptera were observed visiting the flower heads. The visits were mostly by M. bimucronata bees (56.4%). The results allowed to conclude that, although dependent on pollen vectors for reproduction, this is a generalist entomophilous species and, therefore, well adapted to ruderal environments where its presence is prevalent.