Pollen Morphology of Paederia L.(Rubiaceae) from China

The pollen morphology of six species and one variety of Peaderia L. were observed under SEM. The results showed that pollen grains of Peaderia were single, small or medium-sized, radially symmetric and tricolpate, with spheroidal or subprolate in equatorial view and three-lobed circular to obtuse triangular in the polar view, endoaperture absent. The exine ornamentation of pollen grains were perforate, microreticulate or reticulate, spinulescent or not. Pollen dimorphism was found in P. foetida and P. pertomentosa, in which P. pertomentosa was reported for the first time. It was consistent with the previous view that pollen dimorphism is not linked with style heterostyly. The evolutionary trend of exine ornamentation may be in order as: perforate, microreticulate or reticulate →coarsely reticulate; rod-like luminal processes absent → rod-like luminal processes present. The pollen morphological characteristics of Peaderia belong to transition type in Rubiaceae.