title: Morphological, phylogenetic, and ecological diversity of the new model species Setaria viridis (Poaceae: Paniceae) and its close relatives.
abstract: OBJECTIVE
  Species limits of the emerging model organism Setaria viridis (tribe Paniceae, subtribe Cenchrinae) are not well defined. It is thought to be related to S. adhaerens, S. faberi, S. verticillata, and S. verticilliformis and in North America occurs with the morphologically similar S. pumila. An integrated approach was taken to evaluate its variation and relationships with the other taxa.
  
  
  METHODS
  Statistical morphology, flow cytometry, molecular phylogenetics, and growth experiments were employed to examine the group's physical variation, polyploidy, evolutionary relationships, and drought ecology, respectively.
  
  
  RESULTS
  SETARIA VIRIDIS contributed one genome to the tetraploids S. faberi, S. verticillata, and S. verticilliformis; the other genome of the latter two was contributed by S. adhaerens. Setaria pumila is unrelated. Morphologically, S. viridis is most similar to S. faberi, but all tested accessions of S. viridis were diploid, whereas those of S. faberi were all tetraploid. Principal component analysis of 70 morphological characters consistently separated S. viridis from S. faberi, largely by spikelet characters. The diagnostic morphological characters are not affected by watering. Setaria faberi is far more sensitive to drought, in terms of mortality and morphological stunting, than S. viridis or S. pumila.
  
  
  CONCLUSIONS
  SETARIA VIRIDIS is a diploid species and has contributed to several polyploid derivatives. The most morphologically similar of the polyploids is S. faberi, which differs in spikelet features, phylogenetics, genome size, and ecological response to drought. Researchers using field-collected S. viridis as a model organism will benefit from the clear delimitation provided in this study.
authors.affiliation: Department of Biology, University of Missouri-St. Louis, One University Boulevard, St. Louis, Missouri 63121, USA.
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Layton
authors.forename: Elizabeth A
authors.initials: EA
authors.lastname: Kellogg
mesh_terms: D001499:Bayes Theorem; D005075:Biological Evolution; D055864:Droughts; D004463:Ecology; D005434:Flow Cytometry; D018745:Genome, Plant / Q000235:genetics*; D015999:Multivariate Analysis; D009656:North America; D010802:Phylogeny; D010940:Plant Proteins / Q000235:genetics; D011123:Polyploidy; D032983:Setaria Plant / Q000033:anatomy & histology / Q000235:genetics* / Q000254:growth & development
chemical_list: D010940:Plant Proteins
keywords: C4; Setaria; drought; polyploidy