Systematics Section / ASPT
Liston, Aaron , Ellison, Nick , Williams, Warren .
Phylogenetic analysis and chromosome evolution in Trifolium (Leguminosae).
TRIFOLIUM, the clover genus, is a morphologically distinctive and economically important member of the legume family. We recently published a phylogenetic analysis based on nuclear ribosomal DNA internal transcribed spacer and chloroplast trnL intron sequences obtained from 218 of the ca. 255 species of Trifolium, representatives from 11 genera of the vicioid clade, and an outgroup Lotus (Ellison et al. 2006. Molecular Phylogenetics and Evolution 39:688-705). Chromosome numbers are known for at least 184 species of clover, and we sampled 177 of these. Over 80% of the species are 2n=16. Aneuploidy (2n=10, 12, or 14) is known from 31 species, eleven of which have both aneuploid and diploid (2n=16) or polyploid counts. Polyploidy is known from 24 species, of which six are exclusively tetraploid, two are hexaploid, and one is dodecaploid (12x). Eleven species have both diploid and polyploid counts, while three have multiple polyploid counts at the tetraploid level and above. Phylogenetic incongruence between the nrDNA and cpDNA results revealed three species of apparent allopolyploid origin: T. dubium, a widespread weed, T. repens, the most commonly cultivated clover species, and T. pannonicum, the species with the highest chromosome number in the genus. The other 20 polyploids are apparently autopolyploid. Character state reconstructions indicate that 2n=16 is the ancestral chromosome number in Trifolium, and infer a minimum of 19 instances of aneuploidy and 22 of polyploidy in the genus. Polyploidy is almost always autapomorphic in Trifolium, while aneuploid events are more likely to demarcate clades. The ancestors of these aneuploid clades may have been polymorphic for diploid and aneuploid chromosome numbers. Alternative explanations require additional origins of aneuploidy or the unlikely reversal from aneuploidy to diploidy.
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Ellison et al. 2006 Molecular phylogenetics of the clover genus (Trifolium—Leguminosae)
1 - Oregon State University, Department of Botany & Plant Pathology, 2082 Cordley Hall, Corvallis, Oregon, 97331-2902, USA
2 - AgResearch, Grasslands Research Centre, Private Bag 11008, Palmerston North, , New Zealand
Presentation Type: Oral Paper:Papers for Sections
Date: Monday, July 31st, 2006
Time: 5:15 PM