POLLEN ULTRASTRUCTURE AND RELATIONSHIPS OF FUSAEA (BAILLON) SAFFORD AND DUGUETIA A SAINT-HILAIRE (ANNONACEAE)

Cladistic analyses indicate that the neotropical genus Fusaea, placed by Walker in his Fusaea tribe along with other genera with large, gran ular tetrad pollen (e.g. Xylopia, Cananga), does not belong with these genera (our xylopioid clade) but rather with several genera with pseu dosyncarpous fruits (Letestudoxa, Duguetia, Pachypodanthium), which to gether with Uvaria and Toussaintia form our uvarioid clade. TEM observ ations show that despite the convergence of its pollen with the xylopi oids at the LM level, Fusaea differs from that group and resembles oth er uvarioids in having a nexine consisting of multiple foliations rath er than fused granules, plus an unusually thick tectum overlying a thi n granular layer. TEM observations confirm that two species of Dugueti a have a highly reduced exine consisting of probable remnants of the t ectum. Cladograms confirm a trend for exine reduction in the uvarioids , with the spines of Pachypodanthium derived from tectal verrucae, as in Letestudoxa and Duguetia. Radiation of the uvarioids was apparently centered in Africa and South America when the South Atlantic was narr ower than it is today.