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.