Pollen and the Evolution of Arctotideae (Compositae) |
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Authors: | Alexandra H Wortley V A Funk John J Skvarla |
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Institution: | (1) Royal Botanic Garden Edinburgh, 20A Inverleith Row, Edinburgh, EH3 5LR, UK;(2) U.S. National Herbarium, Smithsonian Institution MRC 166, P.O. Box 37012, Washington, DC 20013, USA;(3) Department of Botany–Microbiology and Oklahoma Biological Survey, University of Oklahoma, Norman, OK, USA |
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Abstract: | Recent molecular studies have elucidated the phylogeny of Compositae tribe Arctotideae, and found it to contain two, well
supported, monophyletic subtribes, Arctotidineae and Gorteriinae, as well as some polyphyletic and problematic genera. On
the basis of this new information, it may now be possible to identify diagnostic characters and synapomorphies to support
the groupings defined within Arctotideae. Pollen characters have been shown to be particularly variable in Compositae. This
paper aims to investigate the utility of those characters in the context of recent molecular phylogenies, in order to determine
synapomorphic and diagnostic characters in Arctotideae. The pollen of each genus is described, illustrated with scanning electron
micrographs, and optimised on a phylogeny of the tribe. Many pollen characters were found to be very informative when considered
in the context of the current best estimate of phylogenetic relationships. Pollen morphology provides synapomorphies for clades
at a number of hierarchical levels within Arctotideae, including the two subtribes, Arctotidinae and Gorteriinae, the grouping
of Eremothamnus and Hoplophyllum, and smaller clades. It also supports the exclusion of Platycarpha from the tribe. The plesiomorphic palynological state for the tribe is discussed. Particular attention is paid to the evolution
of different patterns of lophae (surface ridges). A single origin for the lophate condition is proposed as the most parsimonious
mode of evolution in Arctotideae. |
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Keywords: | Arctoteae Arctotidinae Asteraceae Characters Gorteriinae Palynology Phylogeny |
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