The historical and recent distribution, ecology and phytosociology of perennial grass Beckmannia eruciformis was studied in Slovakia between 2002 and 2010. Altogether 22 natural and two secondary sites with presence of the species were found from published sources, herbaria and field research. Localities of its native occurrence have been concentrated in Eastern Slovakia (Východoslovenská nížina Lowland from the settlement of Streda nad Bodrogom to the villages of Pribeník and Biel). Secondary sites were found in Western Slovakia (Podunajská nížina Lowland; the surroundings of Sládkovičovo town and Jaslovské Bohunice village). The relatively massive reduction of Beckmannia eruciformis localities was recorded in the seventies and eighties of the last century; it was related to massive land reclamation and alterations in the water regime of river alluvia. Recently only seven localities were found. Permanent occurrence was confirmed only in two localities (Malý Horeš, Strážne). In those cases Beckmannia eruciformis has created relatively large populations including some thousands of individuals. All other recent occurrences were temporary (Streda nad Bodrogom, Keresztúr farmstead, Horešské lúky Nature Reserve, Veľký Horeš, Pribeník). Moreover, they were relatively poor in the number in individuals and are acutely threatened by anthropogenic changes of environmental conditions. According to our results and by applying the IUCN criteria, we propose to modify the threat category of the species from critically endangered (CR) to endangered (EN) in Slovakia. Occurrence of the association Beckmannietum eruciformis and the alliance Beckmannion eruciformis, was also not confirmed for Slovakia during our research. We believe that the association was not present in the past either. Recently, Beckmannia eruciformis was found in the stands of Oenanthion aquaticae (Phragmito-Magnocaricetea) and Potentillion anserinae (Molinio-Arrhenatheretea) in two localities (Malý Horeš, Strážne) during our study. The species composition of the mentioned alliances is fundamentally influenced by the ecological conditions of sites, mainly by water regime during the vegetation period. According to our knowledge, the most favourable conditions for Beckmannia eruciformis are the following: short-term and low floods in the spring, decrease of the water table at the beginning of summer and relatively high level of groundwater during next part of vegetation period. On the contrary, the species may not appear on the site in case of unfavourable weather conditions (dry years).
