A floristic description is presented of the study sites of the Research Training Group “The role of biodi-versity for biogeochemical cycles and biotic interactions in temperate deciduous forests”. To investi-gate different aspects of plant biodiversity in Hainich National Park (Thuringia), deciduous forest stands with low, medium and high canopy tree species diversity were compared. The results of species richness and forest communities show that the research sites are characterised by a typical central European forest flora. Greater vascular plant species richness occurs with higher diversity of tree species. Six of altogether twelve research sites are assigned to the beech forest alliance (Galioodorati-Fagion), the second half belongs to the oak-hornbeam forest alliance (Carpinionbetuli). Suballiances within the Galioodorati-Fagion in the study area include the Galio-Fagetum and the Hordelymo-Fagetum. All Carpinionbetuli relevées are assigned to the suballiance Stellario-Carpinetum.