Waking up from a taxonomist's nightmare: Emerging structure of Ranunculus section Batrachium (Ranunculaceae) in central Europe based on molecular data and genome sizes
Abstract
Ranunculus section Batrachium (water crowfoot) ranks among the most taxonomically challenging aquatic plant groups due to morphological reduction, phenotypic plasticity, polyploidy and reticulate evolution. This study, for the first time in this group, linked morphology, genome size and genetic data (two non-coding regions of plastid DNA and the ITS region of nuclear ribosomal DNA).
This extensive data set, including 258 central European populations, enables us to recognize widespread lineages from hybrids and to trace the evolutionary processes underlying the observed diversity. Most of the traditionally recognized species are supported.
However, the presence of two morphologically cryptic but genetically well-differentiated lineages was detected within Ranunculus trichophyllus, and three separate lineages of different parentage were confirmed in the Ranunculus penicillatus complex. An allopolyploid origin was revealed in Ranunculus aquatilis, Ranunculus baudotii and in both lineages of R. trichophyllus, for which the parentage has not yet been studied, and allopolyploidy is suspected in all other polyploid taxa except for the triploid cytotype of Ranunculus fluitans, which is most likely autopolyploid.
We detected putative F(1) hybrids of seven different parentage combinations, including two involving Ranunculus rionii, representing the first known hybrids of this species. An additional 13 hybrid cytotypes (backcrosses or entailing additional polyploidization) were revealed; c. 20% of Ranunculus peltatus accessions seem to be influenced by introgression detectable only using sequence data.
The Batrachium group is remarkable due to the coexistence of well-defined lineages with recently evolved biotypes arising due to hybridization and polyploidization.