Interspecies hybrids in Carex sect. Ceratocystis (Cyperaceae) of Northwest Russia as revealed by analysis of the internal transcribed spacer (ITS1) and trnL sequences

Carex sect. Ceratocystis is one of the most taxonomically complex groups in the genus. Resolving the phylogeny and systematics of this section is challenging due to frequent interspecific hybridisation and introgression. Most species belonging to this group can produce hybrids, suggesting that species boundaries are semipermeable. To trace hybridisation and introgression among the species of the sect. Ceratocystis from the territory of Northwestern Russia, we studied the intragenomic polymorphism of the internal transcribed spacer (ITS1) of the 35S rRNA genes in Carex flava, C. serotina, C. scandinavica, C. hostiana, and their putative hybrids (C. flava × C. scandinavica, C. flava × C. serotina, C. hostiana × ?) and traced maternal lineages using the chloroplast trnL marker. In addition, we evaluated comparative morphological data and pollen fertility for these taxa. It was found that pure species have a number of species-specific ribotypes, while putative hybrids have a set of ribotypes from different parents. Pure species always had a high percentage of fertile pollen, as did some hybrids, while other hybrids were completely sterile. PCA analysis based on morphology data showed three clusters: C. serotina together with C. scandinavica, hybrids, and C. flava; the same showed PCoA analysis based on molecular data. Comparison of all obtained data supports a hybrid origin of the specimens having intermediate morphology.