Disentangling the taxonomy and ecology of South American Ranunculus subgen. Batrachium

• The number and entity of Batrachium species is a controversial issue in South America.
• The identification of two species is supported by morphological and molecular traits.
• R. aquatilis and R. trichophyllus are segregated by climate but not by water quality.
• No intraspecific molecular variability is found within species.
• Phylogenetics traits suggest a probable alien origin for Batrachium in South America.

The taxonomy and status of white-flowered aquatic Ranunculus (Ranunculus L. subgen. Batrachium (DC.) A. Gray) in South America have been subject of controversy. We examined morphological, ecological and molecular characters of Batrachium populations in the Southern American cone along a latitudinal gradient encompassing two bioclimates: Mediterranean and Temperate. Two species were identified by means of morphological and molecular characters: Ranunculus aquatilis L. and Ranunculus trichophyllus Chaix. These species showed overlapping ranges of water ecological parameters, but with a wider spread than in their ecological behavior in Europe. Species distribution modeling related the occurrence of R. aquatilis to mean diurnal range, altitude, and precipitation of driest quarter and also related the occurrence of R. trichophyllus to mean temperature of driest quarter, precipitation of driest quarter, and precipitation of wettest month. Molecular sequences also indicated that each species is composed of populations of a single clone. Phylogenetic traits related South American Batrachium species with their European relatives, which are genetically variable. Thus Batrachium species can be considered as introduced taxa in South America from a probable long-distance dispersal in two different events with subsequent expansion through the dispersal of clones.