Pollen morphology of Rhynchosia and Eriosema (Fabaceae)
The closely related genera Rhynchosia and Eriosema have tricolporate pollen. Twenty-two species of Rhynchosia and nine species of Eriosema were examined with the light microscope. Most of the species have isopolar-type grains, but 11 species have the hitherto rarely described heteropolar-type pollen, i.e. on a single grain, the ends of the colpi subtend a greater area at one pole than at the opposite pole. Duplicate examination of 13 species indicates that polarity types are constant within those species. While the genera cannot be separated on the basis of pollen morphology alone, there are some pollen characters which embrace most species in any one genus. Eriosema species are mostly heteropolar (67%) and Rhynchosia are predominantly isopolar (77%). The lumina of the reticulum of Rhynchosia tend to be smaller than those of Eriosema and, with one exception, the muri of Eriosema have acute tops while those of Rhynchosia are obtuse. Scanning electron micrographs illustrate pollen morphology.