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The Caucasus harbours unique forest vegetation so far only little studied using the Braun-Blanquet approach. This study is mostly based on a dataset (N = 110) of original phytosociological relevés of oak-hornbeam and ravine forests in the Eastern Greater Caucasus, Georgia. Their unsupervised classification produced seven communities. Five belong to oak-hornbeam forests (order Lathyro-Carpinetalia caucasicae). Of the zonal Caucasian alliance Crataego-Carpinion, the association Corno australis-Carpinetum inhabits valleys of the Greater Caucasus, and Clinopodio umbrosi-Carpinetum is confined to the warm Eastern Greater Caucasus promontories. The association Astrantio maximae-Carpinetum of the alliance Astrantio-Carpinion represents distinctive Caucasian montaneoak-hornbeam forests. The other two communities, documented by a few relevés, were described at the community level only. Within ravine forests (order Aceretalia pseudoplatani), we introduce a new Caucasian alliance Pachyphragmo macrophyllae-Tilion begoniifoliae with two associations. Valeriano tiliifoliae-Ulmetum glabrae comprises Caucasian montane ravine forests whereas Hedero pastuchovii-Aceretum velutini inhabits the foothills of the Eastern Greater Caucasian. To provide a broader context of the recognized communities, an expanded dataset (N = 231) of original relevés and previously published relevés of Georgian deciduous forests was analysed. It indicated a major turnover in species composition following biogeographical patterns presumably driven by macroclimate and vegetation history. [ABSTRACT FROM AUTHOR]

• Glacial survival of Astragalus onobrychis within the Pannonian region. • Pleistocene E–W expansion from the Pontics/Caucasus into Pannonian region (8x). • Younger, smaller-scaled postglacial W–E migration across the Pannonian region. • Long-term stable populations in Dobruja, N Balkan & Central Pontic subregions. • High genetic uniqueness of S Pannonian, N Balkan and N Caucasus populations. Steppe grasslands represent important refuges for rare species in the Pannonian region of eastern Central Europe. Nevertheless, little is known about their regional continuity and potential (post)glacial in-situ survival. Biogeographical studies assume potential source areas for the postglacial (re)colonisation of the Pannonian region in the Western and Central Pontics including the Black Sea coast. However, south-exposed slopes surrounding the Hungarian plain may have also played an important role as small-scale refugia. Using cpDNA sequence markers (atpI-H , rpL16, ycf1) and 190 individuals representing 25 populations, we investigated the genetic diversity and biogeographical history of Astragalus onobrychis within different subregions of its European distribution. We aimed at answering questions about the glacial survival, (post)glacial expansion and/or recent decline of the species throughout this area. A TCS network showed 108 haplotypes, which were divided into two unconnected clusters, representing different ploidy levels. We found octoploid populations widely distributed from the Pannonian region and Transylvania to more eastern areas in the Western Pontics and the Northern Caucasus. On the contrary, di- and tetraploid populations occur in the Dobruja and the Northern Balkan Peninsula, but also in the Central Pontic and the Southern Pannonian subregions. Four main cpDNA haplotype groups basically showed a geographical pattern; the Pannonian region being best-defined. We found high haplotype and moderate to high nucleotide diversity within most populations/subregions. Equilibrating these two genetic diversity measures indicates a long-term – probably glacial – (diploid) persistence of A. onobrychis in the Southern Pannonian subregion, areas along the Black Sea coast, the Northern Balkan Peninsula and the Central Pontic subregion. However, the octoploid lineage likely originated more to the east and expanded to Western Pontic areas and the Pannonian Basin probably already during Pleistocene. [ABSTRACT FROM AUTHOR]