POLLEN MORPHOLOGY AND THE SYSTEMATIC POSITION OF TRIPLOSTEGIA (DIPSACALES)

Triplostegia comprises two species of perennial herbs from southeast A sia, T. glandulifera and T. grandiflora. The systematic position of th e genus has been debated ever since it was described, and it has been placed in either Dipsacaceae or Valerianaceae, or in a family of its o wn Triplostegiaceae. Pollen of Triplostegia, investigated by light mic roscopy and scanning electron microscopy, is similar to that of both D ipsacaceae and Valerianaceae. Presence of numerous branched and bent c olumellae as well as an aperture margin structure resembling the halo found in Valerianaceae indicates a closer relationship to the Valerian aceae. A sister-group relationship between Triplostegia and the Valeri anaceae is furthermore supported by other studies of molecular and mor phological data. In order to maximize information content in the frame work of mandatory classificational ranks, Triplostegia is best include d in the family Valerianaceae, as the sole member of a subfamily Tripl ostegioideae.