Comparison of pollen characters in Lysiostyles Benth. and allied genera (tribe Maripeae - Convolvulaceae)

Pollen morphology and ultrastructure was studied for the monotypic genus Lysiostyles (Convolvulaceae, tribe Maripeae) distributed in Guyana, Suriname and Venezuela. Lysiostyles scandens is a liana with alternate leaves, thyrsiform inflorescence, white corolla with acuminate lobes, five epipetalous stamens, anthers with elongated connectives and a superior ovary with two carpels. The styles are glabrous, branched and divided at the base with cylindrical stigma and lignified and indehiscent fruits. Pollen was collected from specimens in the herbaria RB, L, and U. For observation under light microscopy (LM) and scanning electron microscopy (SEM), pollen grains were prepared using acetolysis. Non-acetolysed pollen grains were prepared for observation by transmission electron microscopy (TEM). Pollen is small to medium sized, isopolar, mostly subprolate, and subcircular amb, tricolpate and tectate with a wavy relief and microechinate tectum. The sexine is thicker than the nexine. The pollen features observed in Lysiostyles are important for the characterisation of the genus, as well as for understanding relationships within the tribe Maripeae (Dicranostyles and Maripa), and support patterns suggested by phylogenetic studies.