Evolutionary patterns and processes in the genus Potentilla L. (Rosaceae)

Abstract

Firstly, a reconstruction of phylogenetic relationships based on three chloroplast (cp) DNA markers comprising 98 species of the genus Potentilla and 15 additional genera from the tribe Potentilleae (Rosaceae) is presented. The phylogeny supported the current generic concept of two subtribes (Fragariinae and Potentillinae), and resolved major lineages within the subtribe Potentillinae, comprising also taxonomically highly diverse but molecularly little diverged core group of Potentilla. Age estimates of phylogenetic splits resolved in the Potentilleae using Bayesian inference, suggested a diversification of the tribe in the Eocene and radiation of two major evolutionary lineages (subtribes) at approximately comparable times. Ancestral area reconstructions based on the recent distribution ranges suggested an Asian origin for Potentilla s.str., and explained its arrival in Europe and particularly in North America by multiple dispersal events. The combination of the phylogenetic, geographic and fossil record data with inferred time estimates and taxonomy revealed strongly contrasting evolutionary patterns: rapid speciation on a continental and worldwide scale accompanied by multiple intercontinental dispersals opposing to the largely diverged lineages of limited taxonomic diversity and vicariant geographic distribution. Furthermore, hybridisation and polyploidisation as drivers of speciation were identified in two case studies of restricted taxonomical and geographical coverage. Combined analysis of AFLPs, cpDNA sequences and ploidy levels, used in a case study of P. argentea group in Europe, identified four main lineages within the Potentilla argentea group, revealing two ploidy levels. Allopolyploid origin was confirmed for the hexaploid P. argentea, which apears to be apomictic. The diploid P. argentea is a self‐pollinator with a highly reduced genetic variability and P. calabra is reproducing sexually. A Late Quaternary migration route from Iberian Peninsula throughout the western Europe to Scandinavia and probably also farther to the Baltic region was suggested for the diploid P. argentea and no clear geographical patterns were detected for the hexaploid P. argentea, most probably due to independent immigration of genetically divergent lineages, which resulted in an overlap of several immigration routes. Finally, P. alpicola and P. collina populations in the South Tyrol were examined. On one hand, P. argentea and P. pusilla have been identified as parental taxa for the apomictic P. alpicola. On the other hand, apomictic P. collina populations are regarded rather as recent derivatives of the hexaploid P. argentea. Studied populations seem to evolve multiply, at each locality separately, however some populations share similar evolutionary history.