The genus Stipa L. comprises over 150 species, all native to the Old World, where they grow in warm temperate regions throughout Europe, Asia, and North Africa. It is one of the largest genera in the family Poaceae in Middle Asia, where one of its diversity hotspots is located. However, identification of Middle Asian Stipa species is difficult because of the lack of new, comprehensive taxonomic studies including all of the species recorded in the region. We present a critical review of the Mid-Asian representatives of Stipa, together with an identification key and taxonomic listing. We relied on both published and unpublished information for the taxa involved, many of which are poorly known. For each taxon, we present a taxonomic and nomenclatural overview, habitat preferences, distribution, altitudinal range, and additional notes as deemed appropriate. We describe four new nothospecies: S. ×balkanabatica M. Nobis & P. D. Gudkova, S. ×dzungarica M. Nobis, S. ×pseudomacroglossa M. Nobis, S. ×subdrobovii M. Nobis & A. Nowak, one subspecies S. caucasica Schmalh. subsp. nikolai M. Nobis, A. Nobis & A. Nowak, and eight varieties: S. araxensis Grossh. var. mikojanovica M. Nobis, S. caucasica var. fanica M. Nobis, P. D. Gudkova & A. Nowak, S. drobovii (Tzvelev) Czerep. var. jarmica M. Nobis, S. drobovii var. persicorum M. Nobis, S. glareosa P. A. Smirn. var. nemegetica M. Nobis, S. kirghisorum P. A. Smirn. var. balkhashensis M. Nobis & P. D. Gudkova, S. richteriana Kar. & Kir. var. hirtifolia M. Nobis & A. Nowak, and S. ×subdrobovii var. pubescens M. Nobis & A. Nowak. Additionally, 12 new combinations, Achnatherum haussknechtii (Boiss.) M. Nobis, A. mandavillei (Freitag) M. Nobis, A. parviflorum (Desf.) M. Nobis, Neotrinia chitralensis (Bor) M. Nobis, S. badachschanica Roshev. var. pamirica (Roshev.) M. Nobis, S. borysthenica Klokov ex Prokudin var. anomala (P. A. Smirn.) M. Nobis, S. holosericea Trin. var. transcaucasica (Grossh.) M. Nobis, S. kirghisorum P. A. Smirn. var. ikonnikovii (Tzvelev) M. Nobis, S. macroglossa P. A. Smirn. var. kazachstanica (Kotuchov) M. Nobis, S. macroglossa var. kungeica (Golosk.) M. Nobis, S. richteriana var. jagnobica (Ovcz. & Czukav.) M. Nobis & A. Nowak, and S. zalesskii Wilensky var. turcomanica (P. A. Smirn.) M. Nobis are proposed, and the lectotypes for 14 taxa (S. arabica Trin. & Rupr., S. bungeana Trin. ex Bunge, S. caspia K. Koch, S. ×consanguinea Trin. & Rupr., S. effusa Mez, S. ×heptapotamica Golosk., S. jacquemontii Jaub. & Spach., S. kungeica Golosk., S. margelanica P. A. Smirn., S. richteriana, S. rubentiformis P. A. Smirn., S. sareptana A. K. Becker, S. tibetica Mez, and Timouria saposhnikovii Roshev.) are designated. In Middle Asia the genus Stipa comprises 98 taxa, including 72 species, four subspecies, and 22 varieties. Of the 72 species of feather grasses, 23 are of hybrid origin (nothospecies). In Middle Asia, feather grasses can be found at elevations from (0 to)300 to 4500(to 5000) m, but most are montane species. The greatest species richness is observed at altitudes between 1000 and 2500 m. Nineteen species grow above 3000 m, but only nine above 4000 m. The number of taxa (species and subspecies) growing in each country also varies considerably, with the highest noted in Kazakhstan (42), Tajikistan (40), and Kyrgyzstan (35). Of the 76 taxa of Stipa (species and subspecies) recorded in Middle Asia, 41 are confined to the region, with some being known only from a single country or mountain range. Distribution maps of selected species are provided.

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Hybridisation in the wild between closely related species is a common mechanism of speciation in the plant kingdom and, in particular, in the grass family. Here we explore the potential for natural hybridisation in Stipa (one of the largest genera in poaceae) between genetically distant species at their distribution edges in Mountains of Central Asia using integrative taxonomy. Our research highlights the applicability of classical morphological and genome reduction approaches in studies on wild plant species. The obtained results revealed a new nothospecies, Stipa × lazkovii, which exhibits intermediate characters to S. krylovii and S. bungeana. A high-density DArTseq assay disclosed that S. × lazkovii is an F1 hybrid, and established that the plastid and mitochondrial DNA was inherited from S. bungeana. In addition, molecular markers detected a hybridisation event between morphologically and genetically distant species S. bungeana and probably S. glareosa. Moreover, our findings demonstrated an uncertainty on the taxonomic status of S. bungeana that currently belongs to the section Leiostipa, but it is genetically closer to S. breviflora from the section Barbatae. Finally, we noticed a discrepancy between the current molecular data with the previous findings on S. capillata and S. sareptana. Hybridisation in the wild between closely related species is a common mechanism of speciation in the plant kingdom 1-7. Due to the prevalence of polyploidy found in angiosperms it has been estimated that around 11% of flowering plants may have arisen through hybridisation events 4. In addition, speciation via hybridisation can lead to an equal ploidy number within parental and newly formed species 3. In general, hybridisation is often accompanied by introgression and causes gene transfer between species via repeated backcrossing 4,8-11. On the one hand it may have contributed to species diversity and speciation 5,12,13 , on the other, deleterious consequences of hybridisation such as decreased fitness, genetic assimilation and gene swamping may drive populations toward the brink of extinction 14-16. In the grass family (Poaceae) hybridisation and introgression are well studied mainly for economically impor