title: Formalizing morphologically cryptic biological entities: new insights from DNA taxonomy, hybridization, and biogeography in the leafy liverwort Porella platyphylla (Jungermanniopsida, Porellales).
abstract: OBJECTIVE
  Recognition and formalization of morphologically cryptic species is a major challenge to modern taxonomy. An extreme example in this regard is the Holarctic Porella platyphylla s.l. (P. platyphylla plus P. platyphylloidea). Earlier studies demonstrated the presence of three isozyme groups and two molecular lineages. The present investigation was carried out to elucidate the molecular diversity of P. platyphylla s.l. and the distribution of its main clades, and to evaluate evidence for the presence of one vs. several species.
  
  
  METHODS
  We obtained chloroplast (atpB-rbcL, trnL-trnF) and nuclear ribosomal (ITS) DNA sequences from 101 Porella accessions (P. platyphylla s.l., P. × baueri, P. cordaeana, P. bolanderi, plus outgroup species) to estimate the phylogeny using parsimony and likelihood analyses. To facilitate the adoption of Linnean nomenclature for molecular lineages, we chose a DNA voucher as epitype.
  
  
  RESULTS
  Phylogenies derived from chloroplast vs. nuclear data were congruent except for P. platyphylla s.l., including a North American lineage that was placed sister to P. cordaeana in the chloroplast DNA phylogeny but sister to the Holarctic P. platyphylla s.str. in the nuclear DNA phylogeny. European and North American accessions of P. cordaeana and P. platyphylla form sister clades.
  
  
  CONCLUSIONS
  The genetic structure of P. platyphylla s.l. reflects morphologically cryptic or near cryptic speciation into Holarctic P. platyphylla s.str. and North American P. platyphylloidea. The latter species is possibly an ancient hybrid resulting from crossings of P. cordaeana and P. platyphylla s.str. and comprises several distinct molecular entities.
authors.affiliation: Department of Systematic Botany, Albrecht-von-Haller-Institute of Plant Sciences, Georg-August-University, Untere Karspüle 2, 37073 Göttingen, Germany. jheinri@uni-goettingen.de
authors.forename: Jochen
authors.initials: J
authors.lastname: Heinrichs
authors.forename: Hans-Peter
authors.initials: HP
authors.lastname: Kreier
authors.forename: Kathrin
authors.initials: K
authors.lastname: Feldberg
authors.forename: Alexander R
authors.initials: AR
authors.lastname: Schmidt
authors.forename: Rui-Liang
authors.initials: RL
authors.lastname: Zhu
authors.forename: Blanka
authors.initials: B
authors.lastname: Shaw
authors.forename: A Jonathan
authors.initials: AJ
authors.lastname: Shaw
authors.forename: Volker
authors.initials: V
authors.lastname: Wissemann
mesh_terms: D002467:Cell Nucleus / Q000235:genetics; D018742:DNA, Chloroplast / Q000235:genetics*; D018744:DNA, Plant / Q000235:genetics*; D021903:DNA, Ribosomal Spacer / Q000235:genetics; D014644:Genetic Variation; D035926:Hepatophyta / Q000145:classification / Q000235:genetics*; D006824:Hybridization, Genetic; D016013:Likelihood Functions; D009656:North America; D010802:Phylogeny; D058974:Phylogeography; D017422:Sequence Analysis, DNA; D013045:Species Specificity
chemical_list: D018742:DNA, Chloroplast; D018744:DNA, Plant; D021903:DNA, Ribosomal Spacer