Pollen morphology of Strobilanthes Blume (Acanthaceae) from southern India and Sri Lanka

Acetolysed pollen from 66 of 74 species of Strobilanthes Blume from southern India and Sri Lanka were examined using light and scanning electron microscopy. Pollen descriptions, scanning electron micrographs, and a key are provided. Two shape classes have been distinguished, spheroidal and ellipsoid (prolate/subprolate). All ellipsoid pollen grains are tricolporate and have pseudocolpi. Six ellipsoid pollen types have been recognised based primarily on differences in rectal ornamentation. Sixteen spheroidal pollen types have been recognised based on variation in number, distribution and form of apertures, and on sexine structure. The current study has shown that variation in pollen morphology is much greater than was previously described, and that the pollen morphology of many species was incorrectly described by Bremekamp (1944). Bremekamp split Strobilanthes s.l. into 54 genera, and made extensive use of pollen morphological characters for generic delimitation. The results of the current study highlight fundamental problems with Bremekamp's classification and demonstrate the necessity of very extensive sampling and rigorous empirical investigations to resolve problems of generic delimitation in large, species rich groups