Posidonia oceanica is a very unique, endemic to the Mediterranean sea, water plant. It has similar features to the terrestrial plants, such as roots, stem and leaf rhizomatous shaped ribbon to a meter long. Also flowers, underwater, and produces fruits that float. But what is really interesting is that form underwater meadows that are home to a rich biodiversity and are ecologically important. It is therefore considered this underwater plant as a good bioindicator of the quality of coastal waters.