Natural hybridization within the genusCallitrichein Sweden was studied on the basis of herbarium material and field studies. One triploid (2n = 15) hybriditaxon is locally common in Scania, S Sweden, where it is shown to be longlived and to disperse vegetatively to form large clones. The triploid and its derivatives are described as a nothospecies under the name ofCallitriche × vigens.Its characteristics, parentage and affinities to Central European hybrids is discussed. As putative parent species, C.platycarpa(2n = 20) andC. cophocarpa(2n = 10) are indicated. The hybrid betweenC. platycarpaandC. hamulata(2n = 29) and a putative hybrid betweenC. platycarpaand C.stagnaliswere only encountered once each and believed to be shortlived
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