Waking up from a taxonomist’s nightmare: emerging structure ofRanunculussectionBatrachium(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 F1 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.

Extensive hybridization in Ranunculus section Batrachium (Ranunculaceae) in rivers of two postglacial landscapes of East Europe

“…aquatilis samples from Croatia and Poland but share the plastid DNA of haplotypes A (haplotype of the R . peltatus group sensu Koutecký et al 5 ) together with all our R . fluitans , R .…”

“…Cook 6 , 14 assumed all members of Batrachium to be potentially capable of hybridization, which is supported by recent studies 1 , 4 , 5 , 15 . Batrachium hybrids can be partly or fully fertile 1 , 3 – 6 , 14 , 16 , which can have important evolutionary implications for the reticulate evolution of the group.…”

“…The group is regarded as one of the hardest to identify among aquatic plants 2 . In addition to limited diagnostic characters, species delimitation and identification are affected by extreme phenotypic variability, frequent hybridization and polyploidy 1 , 3 – 5 .…”

“…In Batrachium, hybridization significantly increase taxonomic diversity [ 6 – 13 ] and is one of the main factors of speciation 1 , 3 – 5 .…”

“…For the identification of Batrachium , a large set of morphological characteristics should be considered, but in many cases, additional molecular genetic data complemented by karyological and genome size results can be valuable or even necessary. Despite the wide application of molecular marker polymorphisms for the detection and confirmation of hybrids in several aquatic plant groups, this approach is still uncommon in Batrachium 4 , 5 , 10 – 13 , 29 , 30 . This is due to both the poorly known diversity of Batrachium in many regions as well as the underestimation of the role of hybridization and polyploidization in the evolution of the section.…”