Webster, Grady L., & Kevin J. Carpenter. Section of Evolution and Ecology, University of California, Davis. Pollen morphological characters as phylogenetic markers in neotropical taxa of Phyllanthus (Euphorbiaceae). Over 800 species of Phyllanthus have been classified into 10 subgenera with over 30 sections, but the broad scope of variation has made it difficult to define monophyletic groups. Pollen morphological studies have provided clues to phylogenetic relationships, but have dealt mainly with Old World taxa. In the present study, pollen morphology has been illustrated (using SEM) of 22 American species in 11 sections. Pollen in subgenus Conami is of special interest because of reductions of apertures and exine ornamentation (pilate in most species). In subgenus Xylophylla, the spectacular development of clypeate grains (with exine shields defined by distinct muri) provides the most useful synapomorphy for defining this group of 80 species. An even more remarkable occurrence of clypeate pollen, with very small exine shields, occurs in section Cyclanthera; it remains unclear whether this indicates a common origin with subgenus Xylophylla. .

Key words: Euphorbiaceae, exine shields, neotropical, Phyllanthus, pollen morphology