Systematics Section / ASPT
Doyle, James A. .
Molecular phylogenies and pollen evolution in Annonaceae (Magnoliales).
THE remarkable diversity of pollen morphology in Annonaceae has attracted evolutionary and systematic attention since the light microscopic, SEM, and TEM studies of Walker and Le Thomas. Phylogenetic analyses of morphological and rbcL data by Doyle, Le Thomas, and Bygrave were used to test hypotheses of pollen evolution, but these need reevaluation in light of more detailed and well-resolved molecular phylogenies. Optimization of pollen characters on molecular trees confirms the ancestral status of granular monosulcate pollen, as in the basal genus Anaxagorea, the near-basal ambavioid clade, and the closest outgroups. However, granular exine structure is derived in the context of angiosperms as a whole, and this character is rather homoplastic within Annonaceae. Because some columellar taxa (Annickia, Bocageeae) are more basal than previously thought, it appears that columellar structure reoriginated in the common ancestor of the MPM (SBC) and “inaperturate” (LBC) clades, which make up most of the family, but several reversals to granular structure occurred within both clades. In the MPM clade, most miliusoids are united by loss of the sulcus and a shift to a verrucate tectum; disulculate pollen is less common and no longer appears to be a synapomorphy of miliusoids as a whole. It is equivocal whether permanent tetrads are a synapomorphy of the “inaperturate” clade or arose several times within it, as well as in isolated lines elsewhere, but tetrads clearly reverted to monads in Isolona and uvarioid lianas. Recognition by Tsou and Fu that microspores undergo rotation in tetrads and polyads of Annona and Cymbopetalum implies that the proximal thin area in these taxa is homologous with a distal sulcus, so that a sulcus persisted longer in the “inaperturate” clade than previously thought, but developmental studies of other groups with tetrads are needed to clarify the significance of this phenomenon.
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1 - University of California, Davis, Section of Evolution and Ecology, One Shields Ave., Davis, California, 95616, USA
Presentation Type: Oral Paper:Papers for Sections
Date: Monday, July 31st, 2006
Time: 8:15 AM