Ranunculus schmalhausenii (section Batrachium, Ranunculaceae), a neglected water crowfoot endemic to Fennoscandia—a case of rapid hybrid speciation in postglacial environment of North Europe

Abstract

The taxa of Ranunculus section Batrachium (Ranunculaceae) have been variably and unsatisfactorily treated in North Europe. Since the description of Ranunculus schmalhausenii (Batrachium dichotomum), probably the most common species in the area, its taxonomic status and identity have been unclear and differently implied. In the majority of treatments, individuals of R. schmalhausenii were ascribed to R. peltatus but sometimes also to the other morphologically similar, heterophyllous taxa. Based on detailed morphological study combined with geographical, ecological and biological evaluation the separate species status of this taxon was finally evidenced. The additive ITS polymorphism pattern of R. schmalhausenii confirmed its hybridogenous origin, however identification of the parental species was impeded by the heterogeneous character of the polymorphism detected. Genetic variation expressed by R. schmalhausenii samples may provide evidence of its multiple origin and suggests sexual reproduction of the taxon. Analysis of a sequence variation of two noncoding cpDNA regions, namely psbE-petL and rpl32-trnL, showed that individuals of R. schmalhausenii inherited cpDNA from two lineages of Batrachium, indicating that this taxon was created at least in two separate hybridization events. Ranunculus schmalhausenii may have originated from sexual ancestral species as multiple created hybrids which have been stabilized by polyploidisation. Genetic structure of R. schmalhausenii is somehow similar to also hybridogenous R. penicillatus. In this study, a detailed morphological, geographical, ecological, and biological description of R. schmalhausenii was presented and the differences between this species and similar taxa were outlined. The name was lectotypified and its synonymy was provided. In contrast to many other heterophyllous species of Ranunculus section Batrachium, R. schmalhausenii occurs mainly in young, postglacial landscapes of Fennoscandia, prefering deep and clear waters with current or wave action and a hard bottom, which perfectly corresponds with a relict, postglacial nature of the species. The species probably presents an example of rapid hybrid speciation (less than 10 000 years) in postglacial environment of North Europe and may be considered as endemic to Fennoscandia. Moreover, R. schmalhausenii, as a weak competitor and pollution sensitive taxon, can be regarded as an indicator of clean waters. Phylogenetic relations within section Batrachium indicates convergent evolution of some species and two cases of possible cpDNA capture.

Cytotype variation, cryptic diversity and hybridization in Ranunculus sect. Batrachium revealed by flow cytometry and chromosome numbers

“…However, the cryptic variation in the R. trichophyllus group may be even more complex. Recent molecular studies revealed four haplotypes and five ribotypes within this species, some of them seemingly unrelated (Zalewska-Gałosz et al 2014, Bobrov et al 2015. In addition, a sample of R. trichophyllus B from low elevations in the Alps (B14-119) had a markedly larger genome size than other samples assigned to this cytotype, which raises doubts about their taxonomic homogeneity.…”

“…Among species of water-crowfoots, the largest 1Cx-values are for the pair of diploid species, R. circinatus and R. rionii, which corresponds to their isolated phylogenetic position in the sect. Batrachium (Bobrov et al 2015). Monoploid genome sizes may also reflect the origin of polyploids, i.e.…”

“…Despite this group showing notable morphological and ecological diversity as a result of various evolutionary processes, only a few biosystematic studies have included Batrachium since Cook's comprehensive monograph (Cook 1966). Recent molecular studies of European water-crowfoots are mostly confined to small regions and only three studies employed molecular markers to analyse genetic variation of more than two species (British plants by Telford et al 2011, Polish plants by Zalewska-Gałosz et al 2014 and north-European plants by Bobrov et al 2015, all of them using a combination of cpDNA and the ITS region). Despite their limited scope, all three studies reveal substantial genetic variation in the morphologically strongly reduced species R. trichophyllus.…”

“…Hörandl et al 2005, Emadzade et al 2010, Hörandl & Emadzade 2012. The reticulate evolution of Batrachium, however, makes research on its phylogeny very difficult (Hörandl & Emadzade 2012, Bobrov et al 2015).…”

Molecular evidence for hybridization between invasive Solidago canadensis and native S. virgaurea

“…Although nrDNA genes undergo concerted evolution relatively quickly (e.g., Fuertes Aguilar et al 1999), additive polymorphism pattern detected in the ITS region has been successfully used in the previous studies on interspecific hybridization in many different genera of plants (e.g., Soltis et al 1995;Zalewska-Gałosz and Ronikier 2012;Zalewska-Gałosz et al 2014;Bobrov et al 2015). A lack of any signs of recombination or homogenization between both parental ITS ribotypes may suggest relatively recent forming of hybrid individuals and/or lack of generative propagation.…”