New findings on Pandanus sect. Imerinenses and sect. Rykiella (Pandanaceae) from Madagascar

Pandanus imerinensis from the east coast of Madagascar was, until recently, assigned to sect. Rykiella but many characters distinguish this species from other taxa found in the section (non-deciduous spiniform stigmas, habit and micromorphology). This species has been placed in the monospecific section Imerinenses. Pandanus macrophyllus, another outstanding species from the east coast is therefore the only species found in section Rykiella. Their taxonomic positions remain unclear. Recently, a staminate plant of P. imerinensis and a mature pistillate plant of P. macrophyllus has been found. These discoveries greatly extend our knowledge of these outstanding species. The staminate flower and pollen morphology of P. imerinensis, the mature pistillate plant of P. macrophyllus are here described for the first time. The taxonomic relationships within the genus are discussed as well as their important role in Indian Ocean biogeography. A key to the spiniform stigmas species of Pandanus in Madagascar is presented.