Systematics Section / ASPT
Doust, Andrew N , Penly, Anya , Jacobs, Surrey , Kellogg, Elizabeth .
Congruence, conflict and polyploidization in the.
The "bristle clade" is a monophyletic group of grasses in subfamily Panicoideae, tribe Paniceae. Members of the clade can be recognized by the sterile branches, called bristles, in the inflorescence, a character that is uniquely derived in this group. The bristles have been lost only once, in the anomalous species "Panicum" bulbosum. To illuminate the history of morphological diversification in this group, and to evaluate the classification of its largest genus, Setaria, we have conducted phylogenetic analyses of the chloroplast gene ndhF, and introns of the nuclear gene KNOTTED1 (KN1). The KN1 introns provide enough variation to distinguish species but still can be aligned among all members of the clade. Our molecular data include ten of the 25 genera previously hypothesized to belong to the bristle clade, and 32 of ca. 300 species. KN1 trees identified five major clades of bristle-grasses: 1) The Pennisetum plus Cenchrus; 2) a morphologically miscellaneous group including Spinifex, Zygochloa, Pseudoraphis, one genome of Paspalidium, and many species of Setaria; 3) Setaria sect. Ptychophyllum plus S. verticillata; 4) Ixophorus plus Panicum bulbosum plus Setaria grisebachii; 5) Paspalidium plus Stenotaphrum. NdhF trees conflicted with the KN1 trees, but the conflicts were localized within the major clades. Setaria is clearly polyphyletic; trees that enforced monophyly of the genus were significantly worse than the maximum likelihood tree. Pennisetum may be paraphyletic, but monophyly cannot be rejected. The dioecious Australian genera, Zygochloa and Spinifex, are sisters, with the Australian Pseudoraphis sister to the pair. ?Panicum? bulbosum is allopolyploid, with three distinct KN1 genes, and multiple bands on Southern blots. The putative maternal genome is the one in clade 4; other parental genomes appear in clades 2 and 3. Sampled species of Paspalidium are tetraploid, with the polyploidization event preceding speciation; the putatively maternal genome falls in clade 2.
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1 - University of Missouri St Louis, Department of Biology, 8001 Natural Bridge Road, St Louis, Missouri, 63121-4499, USA
2 - Royal Botanic Gardens, Mrs Macquaries Road, Sydney, New South Wales, 2000, Australia
nuclear gene phylogeny
Presentation Type: Oral Paper
Location: Salon J - Austin Grand Ballroom/Hilton
Date: Monday, August 15th, 2005
Time: 11:00 AM