Rediscovery of (Cyperaceae) on the northeast periphery of its range in Europe.

In recent years, three large populations of were found in Poland, the richest occurrence of this species in over 30 years. The goal of this research is to determine the habitat factors lead to the mass occurrence of and the present situation of that species and its habitat in Central Europe. Soil conditions of the three populations were studied. To determine the correlation between the occurrence and abundance of species and the chemical parameters of the soil, the DCA and CCA methods were used. The DCA of environmental Ellenberg values was made for all relevés known from Poland. The occurrence of in plant communities in Central Europe was studied. The maximum entropy method was used for potential distribution analysis of . All analyzed traits are important for this species and none has an advantage over another, so the environmental factor affecting the occurrence of is different from the tested. Analysis on Ellenberg values indicate that the longest gradients are temperature, moisture and nutrients. The analysis of vegetation data involving available from Central Europe indicates that this species occurs mainly in the company of and , whereas other species of the Isoëto-Nanojuncetea class appear rarely. In MaxEnt analysis based on bioclimatic variables, the most important variable is BIO1 (Annual Mean Temperature). The results of our observation indicate that anthropogenic factors such as grazing livestock have a positive effect on the occurrence of the species. It is also very likely that the species is promoted by very warm summers with only short periods of heavy rains. A map of the potential distribution of in Central Europe created according historical and future data show an extension of the range of potential habitats to the north and east.