Biogeography and diversification patterns in the Irano‐Turanian biodiversity hotspots inferred from a molecular phylogeny of the subendemic <i>Iris</i> subgenus <i>Scorpiris</i> (Iridaceae)

The Irano‐Turanian Floristic Region harbors a rich flora, but our understanding of the development of this diversity is limited by a lack of data on phylogenetic relationships and biogeographic patterns of endemic and more widespread plants. Hypotheses of in situ diversification versus allopatric diversification were tested using Iris subgen. Scorpiris , a species‐rich group that is widely distributed in this region. Phylogenetic relationships of the subgenus were inferred using a comprehensive sampling strategy that incorporated newly collected accessions that represent previously under‐sampled clades and underrepresented geographical regions. Included was Iris drepanophylla , the type species for a major clade that had not been included in previous Iris studies. Six markers were used, thus increasing plastid region sampling compared to previous studies. The historical biogeography of resolved clades was explored to determine patterns of origin, dispersal, vicariance, and divergence while the RelTime method was used to estimate times of divergence. This study confirmed major clades previously identified in the subgenus, suggested monophyly or non‐monophyly of several species, and revealed unrecognized diversity in two species. Ages of major clades date from the Miocene to the Pliocene, while diversification continued into the Pleistocene. Our biogeographic inferences indicate that the subgenus and most major clades of I . subgen. Scorpiris originated and diversified in the Pamir‐Alay, with subsequent diversification after expansion into the Tian Shan and Irano‐Anatolian regions. Species from one clade dispersed to the Mediterranean and Caucasian regions from the Irano‐Turanian region with relatively little diversification. We conclude, diversification of I . subgen. Scorpiris mainly followed the model of dispersal then allopatric diversification mostly through founder events and/or ecological speciation facilitated by general aridification across Eurasia and mountain uplifts that created rain shadows. We hypothesize that their multi‐scaled bulbs facilitated adaptation to seasonally dry conditions that developed with climatic and geological changes.