The posidonia is an underwater plant, and not a type of seaweed. It flowers underwater and forms a vaste seagrass bed essential to the Mediterranean marine ecosystem.
It gets its name from the Greek seagod Poseidon. It grows underwater, and despite what you may think, it is not a seaweed ! It is an underwater flowering plant with roots. Like all plants, its fruit are responsible for its reproduction. The posidoniacae family contains nine species, eight of which can be found on the Australian coastline, while the ninth grows in the Mediterranean Sea. Human pollution and the spread of the seaweed Caulerpa taxifolia are threatening to make it extinct. These dangers have provoked the French authorities to declare it a protected species on the French coast.
The Mediterranean posidonia grows on seabeds up to 40 metres deep. It develops in vaste seagrass beds which constitute a vital ecosystem in the Mediterranean Sea, as these beds provide a place for many animal species to spawn and lay eggs. Posidonia is a vital food source for many herbivorous marine animals. Its rhizome roots give it a grip on the seabed while the movement of its leaves captures sediment and oxygenizes the surrounding area.
The posidonia flowers annually. The buds appear in September and the flowers bloom in October and November. Pollenization is carried out by the currents. It produces fruit in winter after flowering. Its fruit are the size of a green olive and they fall from the plant in May and June. They float on the surface of the water for between 10 and 15 days. The envelope of the fruit then rots and liberates a seed. This seed then either falls to the seabed or germinates. It has been known to reproduce by seeding, but this is quite rare. It normally seeds by cutting.
Did you know ?
- The Posidonia oceanica is now used as a barometre for judging the quality of the water in the Mediterranean Sea. Since 2000 this plant is observed and then used to evaluate whether the coastline merits a European Union Blue Flag, which is awarded to parts of the coastline deemed clean enough to swim in.
Editor’s Note : At letsGarden.info we include this informative article on the posidonia because it is indeed a plant.