Colloquium: The Utility of Pollen in Systematic and Morphological Studies: A Celebration of the Life of John J. Skvarla
Doyle, James A. .
Evolutionary significance of exine structure in basal angiosperms in the light of phylogenetic analyses.
Phylogenetic analyses based on molecular and morphological data allow more robust inferences on the evolution of exine structure in basal angiosperms. These results contradict many older ideas on directions of evolution, but they reaffirm the systematic value of exine characters. Although the situation in Amborella is somewhat problematic, the ancestral exine structure in angiosperms appears to be columellar, rather than granular or atectate. However, granular structure is important systematically as a synapomorphy of major subgroups in Magnoliales and Laurales. Within Annonaceae, phylogenetic analyses indicate that granular structure was ancestral and columellae were derived one or more times (a reversal to the ancestral state in angiosperms). Exine features - spines set in a reduced granular layer - are among several morphological characters that indicate Lauraceae and Hernandiaceae are more closely related to each other than either is to Monimiaceae, apparently overruling weakly contradictory molecular data. The ancestral angiosperm pollen is inferred to have had a continuous or microperforate tectum, with a reticulate-perforate tectum evolving in the common ancestor of Austrobaileyales and mesangiosperms (all angiosperms other than the ANITA lines). Data on pollen in fossil flowers suggest that reticulate-columellar exines persisted into basal Magnoliales and Laurales, where they are ancestral rather than derived. This suggests that the oldest Early Cretaceous reticulate monosulcates may be closer to the origin of angiosperms than previously believed. Molecular relationships imply that angiosperms originally had a thin endexine, rather than none at all, but without the laminated structure of other seed plants. Development of a foliated nexine appears to unite Magnoliales and Laurales; whether this is foot layer or endexine is partly a problem of definition – whether endexine should be defined in terms of staining or development.
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1 - University of California, Davis, Department of Evolution and Ecology, One Shields Ave., Davis, California, 95616, USA
Presentation Type: Symposium or Colloquium Presentation
Location: Fort Camp Lounge/Gage
Date: Tuesday, July 29th, 2008
Time: 2:15 PM