Morphology, DNA–molecular variation, karyology, ecogeography, and phytosociology suggest allopatric differentiation and species rank for Potentilla rigoana (Rosaceae)

Abstract

AbstractThe Apennines show high floristic diversity promoted by their particular role as an ice–age refugium. However, studies on the evolution of Apennine plants are rare. Potentilla rigoana from the mainly European P. heptaphylla group is an example of a largely ignored taxon originally described from this mountain range. Its evolutionary origin and taxonomic status was studied in an interdisciplinary approach combining morphometric, karyological (flow cytometry and chromosome counting), DNA–molecular (AFLP), ecogeographic (WorldClim climatic variables), and phytosociological data. Morphometric analyses revealed 16 metric and 2 nominal characters separating P. rigoana from its close relatives P. crantzii, P. heptaphylla s.l., and P. neumanniana. Additionally, P. rigoana was intermediate with respect to temperature requirements as well as altitudinal distribution compared to P. crantzii and P. heptaphylla s.l. The species was documented from 54 populations or sampling sites located in the central and southern Apennines where it occurs in montane to subalpine dry habitats. Morphometric analysis suggested its occurrence in the Balkans. Molecular and morphometric analyses further suggested reticulate relationships of the Balkan samples of P. heptaphylla s.l. with P. rigoana. Potentilla rigoana comprises five ploidy levels with the dominant diploids and tetraploids geographically centered in the southern and central Apennines, respectively. The existence of diploids and a uniformly heptaploid population indicate the occurrence of both sexuality and apomixis. The combined datasets suggested species status for P. rigoana. The ecogeographic distribution indicated an allopatric differentiation of the species within the P. heptaphylla group. The latitudinal separation of diploid and polyploid cytotypes coincided with a glacial refugium in the southern Apennines and more dynamic past climatic conditions in the central Apennines.