Genome sizes and phylogenetic relationships suggest recent divergence of closely related species of the Limonium vulgare complex (Plumbaginaceae)

Limonium vulgare and related species form a complex group, but until now cytological and genetic studies have been based on single species and specific geographical areas. We investigated genome size, karyological and genetic diversity in samples from Western Mediterranean and evaluated the phylogenetic relationships among the species of this complex. Genome size was assessed using flow cytometry on samples from natural populations of L. vulgare, L. maritimum and L. narbonense. Chromosome counts were conducted in plants obtained from seeds collected in the field. The internal transcribed spacer ITS1 of the nuclear rDNAs was used to assess ITS polymorphisms as well as the phylogenetic relationships within the L. vulgare complex. Our analyses showed that all species were tetraploid, with the chromosome number of L. maritimum being presented here for the first time. Significant differences were observed in genome size, with L. narbonense having lower genome sizes than the other two species, and possible aneuploids being detected. Ten new ITS sequences from L. vulgare, L. narbonense and L. maritimum were provided. Most species' populations showed unique ribotypes, and L. narbonense has the highest ribotype diversity. One of the L. maritimum populations presented a closer genetic relationship with L. vulgare, whereas the other two seemed to be more related with L. narbonense. Phylogenetic analyses confirmed that L. vulgare and L. narbonense form a monophyletic group, sister to the remaining Limonium species. Our results put into evidence that the studied species may represent a relatively early stage of divergence.