One Species or Two: A Puzzling Case from Scapaniaceae (Marchantiophyta)

This paper addresses the genetic delimitation of narrowly distributed Scapania magadanica and broadly circumpolar S. kaurinii. The phylogenetic trees based on maximum likelihood and Bayesian inference constructed for one of the most informative loci (ITS1–2) showed that Scapania magadanica was deeply nested within the clade of S. kaurinii. The comparison of the obtained topologies with known strong morphological dissimilarities of two taxa has led to the understanding that this approach does not work. The latter may be due to a widespread variable tentatively ‘ancestral’ species (S. kaurinii) having no joint molecular synapomorphies that would delimit it from the locally distributed derived taxon (S. magadanica). Therefore, the relationships of these two species were evaluated using molecular genetic distances with the Neighbor Net split network and TCS haplotype network. The obtained data have confirmed the speculation above, and it is possible to assume that when the S. magadanica lineage split, S. kaurinii already occupied a rather wide range, which could limit further gene flow among its remote populations.