Molecular confirmation of the hybrid origin of Sparganium longifolium (Typhaceae)

Sparganium longifolium was reported as a hybrid between S. emersum and S. gramineum based on its intermediate type or the common characteristics of its parent species. Its hybrid origin needs to be confirmed using molecular technology. We investigated the origin of S. longifolium based on 10 populations of S. emersum, S. gramineum and S. longifolium from five lakes in European Russia, using sequences of six nuclear loci and one chloroplast DNA fragment. Haplotype network, principal coordinate analysis and genetic clustering based on data of nuclear loci confirmed that S. longifolium is the hybrid between S. emersum and S. gramineum. We found that the natural hybridization between S. emersum and S. gramineum is bidirectional but asymmetrical, and the latter mainly acts as maternal species. We also found that all samples of S. longifolium were F1 generations, and thus hypothesized that S. emersum and S. gramineum could likely maintain their species boundary through the post-zygote reproductive isolation mechanism of F1 generation sterility.