Inferring the potential of plastid DNA-based identification of derived ferns: a case study on the Asplenium trichomanes aggregate in Europe

The utility of three plastid DNA regions to identify fern species was explored with focus on the European representatives of the Asplenium trichomanes aggregate. The sampling included representatives of the three diploid and the four tetraploid taxa recognized in the European flora plus Macaronesia. Besides European samples, the compiled data set comprised specimens of a putative Hawaiian endemic and one species occurring in Southeast Asia. By combining the sequences of three non-coding plastid regions, 13 haplotypes were recovered of which four were found in more than one taxon. Evidences for four distinct diploid lineages were found that correspond to Asplenium anceps , A. inexpectans , A. trichomanes s.s. , and A. tripteropus . The four tetraploids occurring in Europe shared haplotypes with A. inexpectans . Thus, DNA barcoding can successfully identify the diploids, but fail to separate the tetraploids from their diploid ancestors. As a consequence, barcoding analyses of ferns need to take into account the differences of ploidy level measured by evidence independent from the DNA barcode. Evidence for uneven accumulation of intra-species DNA variation was recovered by comparing all species. Furthermore, the study provided evidence that the current taxonomy of these ferns requires to be revised. The two European diploids form well-separated clades and need to be recognized as A. inexpectans and A. trichomanes s.s. To keep name consistency for all European tetraploids, a new name Asplenium jessenii is introduced to replace A. trichomanes subsp. hastatum .