title: Phytogeography of Najas gracillima (Hydrocharitaceae) in North America and its cryptic introduction to California.
abstract: OBJECTIVE
  The discontinuous North American distribution of Najas gracillima has not been explained satisfactorily. Influences of extirpation, nonindigenous introduction, and postglacial migration on its distribution were evaluated using field, fossil, morphological, and molecular data. Najas is a major waterfowl food, and appropriate conservation measures rely on accurate characterization of populations as indigenous or imperiled. •
  
  
  METHODS
  Seed lengths of N. gracillima from native Korean populations, a nonindigenous Italian population, and North American populations were compared using digital image analysis. DNA sequence analyses from these regions provided nine nrITS genotypes and eight cpDNA haplotypes. •
  
  
  RESULTS
  Najas gracillima seeds from Eurasia and California are shorter than those from eastern North America. Nuclear and chloroplast DNA sequences of N. gracillima from Korea and Italy were identical to California material but differed from native eastern North American plants. Eastern North American specimens of N. gracillima at localities above the last glacial maximum boundary were identical or similar genetically to material from the northeastern United States and Atlantic Coastal Plain and Piedmont but divergent from plants of the Interior Highlands-Mississippi Embayment region. •
  
  
  CONCLUSIONS
  In California, N. gracillima is nonindigenous and introduced from Asia. In eastern North America, populations that colonized deglaciated areas were derived primarily from refugia in the Atlantic Coastal Plain and Piedmont. Genetic data indicate initial postglacial migration to northeastern North America, with subsequent westward dispersal into the Upper Great Lakes. These results differentiate potentially invasive California populations from seriously imperiled indigenous eastern North American populations.
authors.affiliation: Department of Ecology and Evolutionary Biology, University of Connecticut, Storrs, Connecticut 06269-3043, USA.
authors.forename: Donald H
authors.initials: DH
authors.lastname: Les
authors.forename: Elena L
authors.initials: EL
authors.lastname: Peredo
authors.forename: Lori K
authors.initials: LK
authors.lastname: Benoit
authors.forename: Nicholas P
authors.initials: NP
authors.lastname: Tippery
authors.forename: Ursula M
authors.initials: UM
authors.lastname: King
authors.forename: Sallie P
authors.initials: SP
authors.lastname: Sheldon
mesh_terms: D001208:Asia; D001483:Base Sequence; D002140:California; D018742:DNA, Chloroplast / Q000737:chemistry / Q000235:genetics; D004272:DNA, Mitochondrial / Q000737:chemistry / Q000235:genetics; D018744:DNA, Plant / Q000737:chemistry / Q000235:genetics; D004275:DNA, Ribosomal / Q000737:chemistry / Q000235:genetics; D005060:Europe; D014644:Genetic Variation; D005838:Genotype; D031321:Hydrocharitaceae / Q000033:anatomy & histology / Q000235:genetics*; D058865:Introduced Species; D008969:Molecular Sequence Data; D009154:Mutation; D009656:North America; D010802:Phylogeny; D058974:Phylogeography; D012639:Seeds / Q000033:anatomy & histology / Q000235:genetics*; D017422:Sequence Analysis, DNA
chemical_list: D018742:DNA, Chloroplast; D004272:DNA, Mitochondrial; D018744:DNA, Plant; D004275:DNA, Ribosomal
keywords: dispersal; genotypes; glacial refugia; nonindigenous; rice culture; seed morphology