CARPENTER, K. J.* and G. L. WEBSTER. Section of Evolution and Ecology, University of California Davis, Davis, CA, 95616. - Evolution of pollen diversity in neotropical Phyllanthus (Euphorbiaceae).
The genus Phyllanthus (Euphorbiaceae), with over 800 described
species of trees, shrubs, and herbs, has a pantropical distribution.
To better understand the range of pollen morphology and its evolution
in the neotropical taxa, and to elucidate their relationships, 22
species from 11 sections have been examined with scanning electron
microscopy. Special attention has been paid to the subgenus
Conami because of its apparent close affinity to the African
subgenus Kirganelia, and the variation in apertures and exine
sculpturing among closely related species. Of particular interest are
clypeate pollen grains, in which the exine is differentiated into
polygonal shields. These are best known in the large subgenus
Xylophylla, with over 80 species; however, a unique type of
clypeate grain has evolved, apparently independently, in section
Cyclanthera. Indeed, the extraordinary grains of P.
lindenianus appear to be unique in the Euphorbiaceae and in all
seed plants. Phylloclade-bearing species of section Xylophylla
in the West Indies have clypeate pollen grains, while
phylloclade-bearing Brazilian species (section Phyllanthus)
have 3-colporate pollen grains with reticulate exine; the pollen
evidence suggests the convergent evolution of similar vegetative
morphologies in neotropical Phyllanthus.
Key words: Euphorbiaceae, Phyllanthus, phylogeny, pollen morphology, scanning electron microscopy