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This work is a study of the organisation and delimitation of the Centaurea stoebe group using molecular methods and to compare them with the results of morphological investigations.
Within the Sect. Acrolophus, the Middle-European species group around Centaurea stoebe L. represents such a case. On one hand, only relatively few morphological characters are present, on the other hand these characters show a high degree of infraspecific variation which complicates the exact delimitation of species.
The Centaurea stoebe group usually includes C. maculosa, C. rhenana, C. muretii, C. vallesiaca and C. stoebe subsp. micranthos which has been introduced from Southeast Europe. In the presence of numerous transitions and hybrids a number of other taxa was included in the investigations. Besides some widely distributed species such as C. paniculata (s.l.) and C. diffusa several endemies (i.e. C. corymbosa, C. dalmatica, C. sagredoi) served as possible outgroups.
For the morphological studies more than 3500 specimens from different herbaria and ca. 1000 additional, freshly collected herbarium specimens from about 200 populations from all over Europe were studied.
The DNA required was extracted from herbarium or silicagel-dried material only, so that rare or plants that are accessible with difficulties only could be included in the investigations.
Chloroplast DNA spacer and internal transcribed spacer (ITS 1 and 2) of the ribosomal repeat of nuclear DNA turned out to be too invariable for phylogenetic analyses within the Centaurea stoebe group. Therefore parts of the distinctly more variable intergenic spacer (IGS) of the ribosomal repeat of nuclear DNA were sequenced. Two regions were developed and established as new markers. By a combination of ITS 1 and the two IGS regions a phylogenetic analysis of the investigation group consisting of 22 taxa was possible. Additionally, RAPD analysis was used to estimate the infraspecific variation and to clarify the origin of introduced plants.