The pollen morphology of 31 species (50 accessions) ofRuelliaL. is described and illustrated, based on examination with light, scanning and transmission electron microscopy. The pollen is spherical, coarsely reticulate (except for two species which are clavate), usually 3-porate, rarely 5-porate or 3-coIporate. Pollen is a good diagnostic character forRuelliaspecies. The pollen characters are discussed with regard to species relationships and functional significance.