A biosystematic study on Ranunculus subgenus Batrachium in S Sweden

A detailed study of Ranunculus subgenus Batrachium was undertaken on material from SW Skåne, S Sweden. 38 populations were sampled including 5 from outside the study area. A comprehensive morphological investigation of the variation pattern, which included biometric analyses, led to a reassessment of diagnostic characters. 64 chromosome counts were made from 28 populations. Minor differences in karyotype constitution between species were demonstrated. Crossing experiments involving 4 species were carried out, and F, was analysed as regards morphology, compatibility, meiosis and seed set. The two diploid species (2n=16), R. fluitans and R. circinatus , are shown to be homogeneous and reproducing vegetatively in S Sweden. The tetraploid R. peltatus is outcrossing and probably self‐incompatible, whereas the likewise tetraploid R. baudotii is self‐compatible and mainly self‐pollinated. These tetraploids are interfertile, but morphologically distinct and kept apart by different ecological demands. Hexaploids, generally referred to two separate species, R. aquatilis and R. trichophyllus , are automatically self‐pollinated in bud (sometimes cleistogamous). All characters used to distinguish these two species are found to be variable and readily modified. Crosses between typical R. aquatilis and typical R. trichophyllus are fully fertile. A division into two species seems untenable. ( R. trichophyllus is treated as conspecific with R. aquatilis ). Semifertile, natural pentaploid hybrid derivates with varying chromosome numbers between R. aquatilis and R. peltatus were found, and have also been experimentally synthesized. The variation pattern in S Sweden deviates in sereral respects from that reported by Cook based mainly on C and W European material.