An updated phylogeny and infrageneric classification of the genus Sisyrinchium (Iridaceae): Challenges of molecular and morphological evidence

Taxon delimitation and classification remains one of the fundamental bases of evolutionary studies and is especially challenging because processes by which new biological entities arise are complex and non-linear over time, although continuous. Sisyrinchium (ca. 140 to 216 taxa) is one of the most species-rich genera of Iridaceae, largely widespread in the Americas. Recent molecular phylogenetic studies have shown that the systematics of the genus is in need of substantial revision. Different data sources were investigated to establish an updated infrageneric classification based on phylogenetic principles. Monophyletic sections of Sisyrinchium were circumscribed using a new phylogenetic framework established from an increased sampling of taxa (107 species), and complementary approaches were combined to provide the most comprehensive infrageneric treatment of the genus proposed so far. Additionally, numerous molecular synapomorphies were identified to reinforce previous taxonomic treatments of tribe Sisyrinchieae (six genera) at the generic level. Major lineages of Sisyrinchium were concordantly resolved with mostly strong to full support by the DNA regions used in the study and ten sections characterized by unique combinations of molecular, morphological and geographical diagnostic characters were recognized. The phylogenetic trees respectively based on plastid + mitochondrial and nuclear ITS DNA regions were generally congruent except for two unplaced species (S. chilense, S. elegantulum) for which ancestral reticulation events were detected. New circumscriptions were provided for seven sections (sect. Cephalanthum, sect. Echthronema, sect. Hydastylus, sect. Segetia, sect. Sisyrinchium, sect. Spathirhachis, sect. Viperella) while three sections (sect. Morphanthus, sect. Rhizilineum, sect. Trichoparcus) were newly described. This work constitutes a robust contribution to elucidate the systematics of Sisyrinchium and emphasizes the need of integrative taxonomic approaches using multiple data sources, not only to improve the delimitation of taxa but also to investigate their evolutionary history.