Palynological contribution to the systematics of Rindera and the allied genera Paracaryum and Solenanthus (Boraginaceae-Cynoglosseae)

The pollen of thirteen species of Rindera, ten of Solenanthus and eight of Paracaryum was examined by light and scanning electron microscopy. Two main pollen types are recognised, one typical of most Rindera species (Rindera tetraspis type) and one occurring in all but one species examined of Paracaryum and Solenanthus (Cynoglossum officinale type). Deviations from the Rindera tetraspis type in Rindera were observed in R. tianschanica, which is characterised by the Cynoglossum officinale pollen type, and R. gymnandra, which shows the Pardoglossum atlanticum type as already published. Within Paracaryum and Solenanthus the only remarkable deviation from the Cynoglossum officinale type was found in Solenanthus hupehensis from China. In the constricted shape and the lack of an ectocingulus, the pollen of this species approaches the Myosotis arvensis type, which is rarely found in the tribe Cynoglosseae. Combined with other morphological peculiarities, pollen characters support the placement of S. hupehensis in a subgenus of its own, S. subg. Silvestria, named after the discoverer of this species.