title: Evolution of cryptic gene pools in Hypericum perforatum: the influence of reproductive system and gene flow.
abstract: OBJECTIVE
  Hypericum perforatum (St. John's wort) is a widespread Eurasian perennial plant species with remarkable variation in its morphology, ploidy and breeding system, which ranges from sex to apomixis. Here, hypotheses on the evolutionary origin of St. John's wort are tested and contrasted with the subsequent history of interspecific gene flow.
  
  
  METHODS
  Extensive field collections were analysed for quantitative morphological variation, ploidy, chromosome numbers and genetic diversity using nuclear (amplified fragment length polymorphism) and plastid (trnL-trnF) markers. The mode of reproduction was analysed by FCSS (flow cytometric seed screen).
  
  
  RESULTS
  It is demonstrated that H. perforatum is not of hybrid origin, and for the first time wild diploid populations are documented. Pseudogamous facultative apomictic reproduction is prevalent in the polyploids, whereas diploids are predominantly sexual, a phenomenon which also characterizes its sister species H. maculatum. Both molecular markers characterize identical major gene pools, distinguishing H. perforatum from H. maculatum and two genetic groups in H. perforatum. All three gene pools are in close geographical contact. Extensive gene flow and hybridization throughout Europe within and between gene pools and species is exemplified by the molecular data and confirmed by morphometric analyses.
  
  
  CONCLUSIONS
  Hypericum perforatum is of a single evolutionary origin and later split into two major gene pools. Subsequently, independent and recurrent polyploidization occurred in all lineages and was accompanied by substantial gene flow within and between H. perforatum and H. maculatum. These processes are highly influenced by the reproductive system in both species, with a switch to predominantly apomictic reproduction in polyploids, irrespective of their origin.
authors.affiliation: Department of Plant Systematics and Biodiversity, Center for Organismal Studies, Heidelberg University, Heidelberg, Germany. marcus.koch@cos.uni-heidelberg.de
authors.forename: Marcus A
authors.initials: MA
authors.lastname: Koch
authors.forename: Charlotte
authors.initials: C
authors.lastname: Scheriau
authors.forename: Anja
authors.initials: A
authors.lastname: Betzin
authors.forename: Nora
authors.initials: N
authors.lastname: Hohmann
authors.forename: Timothy F
authors.initials: TF
authors.lastname: Sharbel
mesh_terms: D054458:Amplified Fragment Length Polymorphism Analysis; D005075:Biological Evolution; D051456:Gene Flow; D014644:Genetic Variation; D006824:Hybridization, Genetic; D020902:Hypericum / Q000033:anatomy & histology / Q000235:genetics*; D011003:Ploidies; D012098:Reproduction; D013045:Species Specificity
keywords: Apomixis; Hypericum maculatum; Hypericum perforatum; St. John's wort; evolution; hybridization; reproductive mode