Pollination biology of a Mandevilla species (Apocynaceae), characteristic of NE-Brazilian inselberg vegetation
Löhne, Cornelia; Mac Hado, Isabel; Cristina Porembski, Stefan; Erbar, Claudia; Leins, Peter
published: Feb 6, 2004
Some features of the reproductive system of Mandevilla spec. (presumably a new species) were investigated in natural populations on granite rock outcrops (inselbergs) in Pernambuco state (NE-Brazil). Field studies included observation of phenological patterns and flower visitors as well as experiments on pollination and fruit set. Additionally, morphology and anatomy of the flowers as well as the pollen tube growth were analysed. Flowers of this Mandevilla species are large, tubular to salverform and very showy due to bright pink colour and exposed presentation on the plant. Although nectar production could not be proved, anatomical studies showed a typical secretory tissue at the base of the gynoecium. Flowers were visited by different species of large bees, but visitation rate - at least during the observation phase - was very low. However, ca. 60 % of the flowers analysed were naturally pollinated and ca. 35 % set fruit. Although autogamy does not occur in unvisited flowers due to strict herkogamy, self-pollination mediated by visiting insects seems possible in the self-compatible flowers. Assuming that insect-mediated autogamy occurs, the high pollen load on the stigma at the end of anthesis can be understood: Even if a bee does not spend much time in the population of Mandevilla investigated, single flower visits may ensure successful pollen transfer. This insect-mediated self-pollination may be interpreted as compensation for the low frequency of flower visitors on inselbergs.