title: Complex patterns of autopolyploid evolution in alfalfa and allies (Medicago sativa; Leguminosae).
abstract: OBJECTIVE
  Although there is growing evidence that autopolyploidy is a widespread and important evolutionary phenomenon, it has received less attention than allopolyploidy. Medicago sativa comprises several diploid and autopolyploid taxa, including autotetraploid cultivated alfalfa, and affords an opportunity to elucidate the evolutionary history of a morphologically and genetically complex autopolyploid system.
  
  
  METHODS
  Phylogenies and haplotype networks were constructed from two chloroplast noncoding regions (rpl20-rps12 and trnS-trnG spacers) across seven diploid and polyploid infraspecific taxa of M. sativa and five additional closely related Medicago species, and genetic differentiation was estimated.
  
  
  RESULTS
  The two most prominent M. sativa autopolyploids have contrasting evolutionary histories. Chloroplast data support a simple autopolyploid origin of subsp. sativa (alfalfa) from diploid subsp. caerulea, from which it is distinguishable in several quantitative characters. In contrast, morphologically identical diploid and autopolyploid cytotypes of subsp. falcata were found to possess very different chloroplast haplotypes, suggesting past introgression from M. prostrata into the polyploid. Despite the presence of hybrids between tetraploid subspecies falcata and sativa, there was little evidence of introgression of chloroplast genomes from either subspecies into the other.
  
  
  CONCLUSIONS
  Autopolyploid evolution in M. sativa is complicated and has followed very different paths in different subspecific taxa. The potential exists for gene flow in virtually all combinations of subspecies both within and between ploidies, yet despite the existence of hybrids, morphologically and genetically distinctive subspecies persist.
authors.affiliation: Cornell University, Ithaca, New York 14853, USA. th263@cornell.edu
authors.forename: Tee
authors.initials: T
authors.lastname: Havananda
authors.forename: E Charles
authors.initials: EC
authors.lastname: Brummer
authors.forename: Jeff J
authors.initials: JJ
authors.lastname: Doyle
mesh_terms: D001483:Base Sequence; D005075:Biological Evolution; D002736:Chloroplasts / Q000235:genetics; D018744:DNA, Plant / Q000235:genetics; D051456:Gene Flow / Q000235:genetics; D006239:Haplotypes / Q000235:genetics; D000455:Medicago sativa / Q000235:genetics*; D010802:Phylogeny; D011123:Polyploidy
chemical_list: D018744:DNA, Plant