Abstract
Marsilea quadrifolia L. (water clover) is a unique species from Romanian flora that belongs to the Marsileaceae family and is one of the most vulnerable plants in Europe due to the loss of its habitats. In this paper, the demographic evolution of a new M. quadrifolia population in the Danube Delta Biosphere Reserve and its natural and anthropic threats are reported. The aquatic fern, M. quadrifolia, has colonized a suitable man-made water body. After a decade of monitoring, the demographic trend is positive but the support capacity of habitat for the water clover remains limited in the long term. The population is vulnerable due to succession of vegetation and its vicinity with a human settlement. The establishment of a micro-reserve represents a suitable method to protect and maintain this threatened M. quadrifolia population.