Reticulate evolution of the critical Mediterranean Gagea sect. Didymobulbos (Liliaceae) and its taxonomic implications

The genus Gagea Salisb. is the largest amongst Liliaceae, including 50-300 species. This genus can be subdivided into at least 14 sections: among them, there is the species-rich, relatively late-branching monophyletic sect. Didymobulbos. Most of species and putative hybrids within this section were included in this study for a total of about 148 accessions (corresponding to 35 taxa), almost all collected across the Euro-Mediterranean area. Thirty-seven morpho-anatomical and ontogenetic characters were considered, together with the cpDNA (trnL-trnF IGS, psbA-trnH IGS) and nrDNA (ITS region) molecular markers. Bayesian analysis revealed the phylogenetic relationships among Didymobulbos taxa, allowing us to demonstrate new circumscriptions of critical species complexes, such as those of G. chrysantha Schult. & Schult.f., G. dubia A. Terracc. and G. granatellii (Parl.) Parl. Also the prominent role played in this section by reticulate evolution is further highlighted: many taxa, often unexpectedly, are inferred to represent hybrids (31 % of investigated taxa). The division into series cannot be maintained as we found extensive molecular evidence of hybridization between them. A new taxonomic setting for Gagea sect. Didymobulbos is proposed, and five new species are described.