THE POLLEN MORPHOLOGY OF HYGROPHILA AND BRILLANTAISIA (ACANTHACEAE, RUELLIEAE)

The pollen morphology of 34 species of Hygrophila R. Br. and 11 species of Brillantaisia P. Beauv. was examined with light, scanning electron, and selectively with transmission electron microscopy. Both genera are characterized by 4-colporate pollen, with the ectexine divided into bands by pseudocolpi, usually 3-4 between each colporus, and a thick, continuous endexine. Nine pollen types and six subtypes are recognized here, on the basis of the sculpturing of the ectexine bands, the number and pattern of the pseudocolpi, and the nature of the endoapertures. Pollen morphology supports the close relationship between Hygrophila and Brillantaisia. Only two species of Brillantaisia have pollen of a type which is not also found in Hygrophila In Hygrophila, pollen morphology indicates groups of species which may be closely related, and there is evidence for differences between Old and New World species.