The two types of growth give rise to the so-called "kill", a terrace formation that consists of a network of strata of rhizomes, roots and trapped sediments.

The leaves arise from orthotropic rhizomes, are cyntiform and bright green in colour that turns brown over time.

The fruit, slightly fleshy and called in some places "sea olive", is similar to a drupe and has a porous pericarp and rich in an oily substance that allows flotation.

When it rots, it releases a seed (coated by a thin membrane, but without a true and proper tegument), which falls to the bottom and, if it finds the right conditions of depth, stability and type of sediment, germinates and gives rise to a new plant.

Asexual reproduction by stolons, which allows the expansion of meadows, is carried out through plagiargiotropic rhizomes, which grow about 7 cm a year and colonise new spaces.

The genus Posidonia is named after Poseidon, the Greek god of the seas, while oceanica refers to its former wide distribution.

Carl Linnaeus gave the first botanical description of this species in Systema Naturae, although the genus was then named Zostera.

The Angiosperm Phylogeny Website concludes that the three families Cymodoceaceae, Posidoniaceae and Ruppiaceae form a monophyletic group.

[7] Posidonia oceanica is a flowering plant which grows in dense meadows or along sandy channels in the waters of the Mediterranean.

This arrangement of the rhizomes eventually forms a mat; the surface contains the active parts of the plant, whereas the center is a dense network of roots and decomposing stems.

Epiphytic communities are consumed by gastropod molluscs, amphipod crustaceans and polychaetes, and play a very important role in the food chain of Posidonia meadows, taking into account the fact that few organisms are able to feed directly from the plant tissue, little appetising for herbivores due to the high percentage [of what?]

In fact, the plant has all the characteristics of a good bioindicator: Therefore, through the study of meadows it is possible to know quite reliably the environmental quality of coastal marine waters.

Generally, the methods of studying Posidonia meadows are four: There is a close relationship between the depth of the lower limit and the transparency of water.

Phenological analyses allow to study different useful parameters to describe the state of health of plants: Lepidochronological analysis consists of the study of the life cycles of P. oceanica leaves, which at the time of their separation, once dead, leave the basal part on the rhizome of the plant.

Many of the compounds reported for P. oceanica were, however, not detected by appropriate phytochemical methods and some most probably represent artifacts and are not genuine natural products of P.

[18]hi Posidonia oceanica has similar characteristics to terrestrial plants, such as roots, rhizomatous stem and cintiform leaves up to one metre long arranged in clumps of 6 to 7.

It constitutes the climax community of the Mediterranean Sea and plays an important role in protecting the coastline from erosion.