PALYNOLOGY, PHYLOGENETIC RECONSTRUCTION, AND CLASSIFICATION OF THE AFRO-MADAGASCAN GENUS ARISTEA (IRIDACEAE)

Examination of the pollen grains of Aristea using light and scanning e lectron microscopy shows that this Afro-Madagascan genus of ca. 50 spe cies is one of the palynologically most diverse genera of the family I ridaceae. Exine sculpturing ranges from reticulate to rugulate to areo late with lumina ranging from large to small. Overall size is also var iable, with grains ranging from medium-sized (45-60 mu m equatorial di ameter) to large (70-97.5 mu m equatorial diameter). Monosulcate apert ures are plesiomorphic, and derived sulculate (apertural membranes obs cured by masses of exine); zonasulculate, 2-zonasulculate, 3-sulcate, and spiral apertures are present in various species. Pollen characters were combined with morphological and anatomical features in a matrix and subjected to cladistic analysis. Trees obtained using successive w eighting procedures were used as the basis for a revised infrageneric classification of Aristea in which three subgenera are recognized. Two subgenera are restricted to the winter-rainfall zone (thr Cape Floris tic Region) of southern Africa, and the third is dispersed widely acro ss sub-Saharan Africa and Madagascar but is barely represented in the Cape Region. Apomorphic character states are discussed in relation to the biology of the genus, and we suggest that some derived aperture ty pes may be adapted to the desiccating climate of the Cape Region.