Oncocyclus irises: phylogeny, evolutionary history and revised taxonomy based on complete chloroplast genome sequences

Abstract

Although Iris sect. Oncocyclus has a long history of recognition as a separate taxon within the genus, its phylogeny and evolution are still poorly understood. In this study, we used plastid genomic data to reconstruct the phylogeny of Oncocyclus, to exam its relationships with other sections of the genus and to shed light on its infrageneric phylogeny, place of origin and evolution. The whole chloroplast genome-based phylogenetic tree constructed for 39 of approximately 43 species and subspecies currently recognized in sect. Oncocyclus resolved sect. Oncocyclus as monophyletic and most closely related to sect. Hexapogon and sect. Regelia. None of the species with infraspecific taxa included in our analysis was monophyletic, casting doubt on the current infrasectional taxonomy. The place of origin of Oncocyclus was found to be Iran, to where its ancestor apparently migrated from an area embracing Central Asia and Afghanistan. The evolutionary line leading to Oncocyclus from the closely related to it Regelia and Hexapogon was associated with a general reduction in number of flowers to one per stem with a concomitant increase in flower size. There were two major migration/expansion routes of Oncocyclus from Iran, namely to the Caucasus and Turkey. Next expansion of Oncocyclus was from southeastern Turkey to Levant. The above strategy of producing large solitary flowers turned out to be very successful in the rocky high elevation and foothill sides of north-western Iran, southeastern Turkey and the Caucasus, but, when they migrated to Levant, also in the deserts and sand dunes of the latter, which led to the rapid colonization of the region and the highest species richness for Oncocyclus among the regions that this group occupies. Based on the phylogenetic tree, a new section, Khorassania, is established and the taxonomic status of many species of Oncocyclus is clarified. In particular, four lower taxa have been elevated to species rank. Four species were treated as unresolved. Three new species from Iran must be established based on living material collected by Frédéric Depalle and maintained in his unique collection.