Visions of the past and dreams of the future in the Orient: the Irano‐Turanian region from classical botany to evolutionary studies

Abstract

Ever since the 19th century, the immense arid lands of the Orient, now called the Irano-Turanian (IT) floristic region, attracted the interest of European naturalists with their tremendous plant biodiversity. Covering approximately 30% of the surface of Eurasia (16000000 km ), the IT region is one of the largest floristic regions of the world. The IT region represents one of the hotspots of evolutionary and biological diversity in the Old World, and serves as a source of xerophytic taxa for neighbouring regions. Moreover, it is the cradle of the numerous species domesticated in the Fertile Crescent. Over the last 200 years, naturalists outlined different borders for the IT region. Yet, the delimitation and evolutionary history of this area remain one of the least well-understood fields of global biogeography, even though it is crucial to explaining the distribution of life in Eurasia. No comprehensive review of the biogeographical delimitations nor of the role of geological and climatic changes in the evolution of the IT region is currently available. After considering the key role of floristic regions in biogeography, we review the history of evolving concepts about the borders and composition of the IT region over the past 200 years and outline a tentative circumscription for it. We also summarise current knowledge on the geological and climatic history of the IT region. We then use this knowledge to generate specific evolutionary hypotheses to explain how different geological, palaeoclimatic, and ecological factors contributed to range expansion and contraction, thus shaping patterns of speciation in the IT region over time and space. Both historical and ecological biogeography should be applied to understand better the floristic diversification of the region. This will ultimately require evolutionary comparative analyses based on integrative phylogenetic, geological, climatic, ecological, and species distribution studies on the region. Furthermore, an understanding of evolutionary and ecological processes will play a major role in regional planning for protecting biodiversity of the IT region in facing climatic change. With this review, we aim to introduce the IT floristic region to a broader audience of evolutionary, ecological and systematic biologists, thus promoting cutting-edge research on this area and raising awareness of this vast and diverse, yet understudied, part of the world.

From species to trait evolution in Aethionema (Brassicaceae)

“…Aethionema species occur mainly at the potential Brassicaceae centre of origin: the Irano-Turanian region (Al-Shehbaz 2012, Couvreur et al 2010, Franzke et al 2011, Warwick et al 2010, Hedge 1976). The Irano-Turanian region harbours three major global biodiversity hotspots (Manafzadeh et al 2016). Aethionema species occur on steep (mostly rocky) slopes between 500-3000m, have simple sessile leaves, are annual or perennial, can be diploid or polyploid and have mainly dehiscent fruits, although heterocarpism also occurs (Davis 1965, Hedge 1965, and one nickel hyperaccumulator, Ae.…”

“…The Irano-Turanian region harbours three main global biodiversity hotspots (Manafzadeh et al 2016, Micó et al 2009, Takhtajan 1986). With ~900 species, this region is also one of world's hotspots for Brassicaceae diversity (Koch & Kiefer 2006).…”

“…The formation of the Alborz, Zagros and Kopeh-Dagh mountain ranges in Iran and the Taurus and Pontic mountain ranges in Turkey are all part of the Alpine orogeny, due to collisions of the African and Arabian plates with the Eurasian plate (Karl & Koch 2013, Davis 1971. In particular the collision of the Arabian plate with the Eurasian plate during the Miocene accelerated the uplift of the Alborz, Zagros and Kopeh-Dagh mountains and the lifting of the Iranian and Anatolian plateaus (Manafzadeh et al 2016). The formation and uplift of these areas caused an aridification of the Irano-Turanian region.…”

“…Aethionema occurs mainly in the western Irano-Turanian region (Hedge & Davis, 1965;Manafzadeh et al, 2016), the hypothesized but not proven centre of origin for Brassicaceae , Couvreur et al 2010, Franzke et al 2011, Warwick et al 2010, Hedge 1976. Aethionema species have ovate to linear leaves, are mainly perennial (though five species are annual) have mainly angustiseptate (flattened parallel to septum) dehiscent fruits (though some species also have indehiscent fruits making them heterocarpic) and some species produce spines Prantl, 1891).…”

“…Heterocarpy is defined as the occurrence of two types of fruits on the same infructescense whereby the fruits and seeds differ in size, colour, shape, dormancy and germination , Imbert 2002 Aethionema arabicum is native to the stony slopes across the Irano-Turanian region with its most Western and Northern border being Bulgaria (Velchev 2015). The Irano-Turanian region harbours three biodiversity hotspots and is at the interface of the Mediteranean, Saharo-Sindian and Euro-Siberian regions containing 32,000 endemic species (Takhtajan 1986, Manafzadeh et al 2016, Davis 1965. In the western Irano-Turanian region a floristic break occurs that connects the south-western Turkish mountains with the north eastern Iranian mountains: the Anatolian Diagonal (Davis 1965).…”