Biogeography of subgenus Iris section Iris
To test the hypothesis that the Caucasus was the area of origin for section Oncocyclus.
A phylogenetic tree using 33 taxa of subgenus Iris section Oncocyclus was developed based on nucleotide sequences of one nuclear and six plastid markers. The resulting tree was used to test biogeographical scenarios. Each species included in the study was assigned to one or more of four geographic areas, Caucasus, eastern Mediterranean, Central Anatolia, and Central Asia. Outgroup taxa included in this study represent three other sections in subgenus Iris and largely occur in Central Asia.
Six models were used to determine likely ancestral area for each node of the phylogenetic tree based on the current distributions of taxa. These models were implemented and compared in the R package BioGeoBEARS. The statistical likelihood that results fit the data were compared across models resulting in the best fit for the model that included dispersal, extinction, speciation, and founder effect speciation in explaining the ancestral areas for the area where ancestors (represented by nodes on the tree) were likely to have occurred. Pie charts were drawn based on probability values for ancestral area estimation at each node. Each area contributing > 10% probability to ancestral area estimations for section Oncocyclus is shown in pie charts on tree. Blank (white) segments represent, collectively, areas contributing < 10% probability.
Biogeographical analyses suggest that the Caucasus is the likely ancestral area for section Oncocyclus (> 75% probability). The Caucasus is bordered by the Black and Caspian Seas and comprises the countries of Georgia, Armenia, Azerbaijan, the most southern portion of Russia, the northwestern part of Iran, and the northeastern portion of Turkey. This area is considered a biodiversity hotspot and is a likely corridor for plant migration between Asia and Europe. The sister lineage to section Oncocyclus is section Hexapogon, represented here by I. longiscapa. This section occurs in Central Asia and the Caucasus from northwestern Pakistan north through central Asia to southern Russia and northeastern Iran.
The area of highest species diversity for section Oncocyclus is the eastern Mediterranean, especially Syria, Jordan, Israel, and Lebanon. It is likely (> 50% probability) that the eastern Mediterranean is the area of diversification for most taxa in section Oncocyclus. There is also a general trend of diversification from the north in western Syria (e.g., I. kirkwoodiae, I. basaltica, I. damascena, and I. antilibanotica) to the south in Israel, Lebanon, and The Palestinian Authority (e.g., I. lortetii, I. atropurpurea, I. petrana, and I. hermona)
Section Oncocyclus is likely to have originated in the Caucasus and spread to the southeast and when it reached the eastern Mediterranean the rate of speciation increased making this region particularly important in the diversity present at this time.
Refer to Wilson, C. A., J. Padiernos and Y. Sapir. 2016. The royal irises (subgenus Iris section Oncocyclus): plastid and low-copy nuclear data contribute to an understanding of their phylogenetic relationships. Taxon 65: 35–46.