Posidonia oceanica (L.) Delile

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포시도니아과(Posidoniaceae)

Posidonia oceanica, commonly known as Neptune grass or Mediterranean tapeweed, is a seagrass species that is endemic to the Mediterranean Sea. It forms large underwater meadows that are an important part of the ecosystem. The fruit is free floating and known in Italy as "the olive of the sea" (l'oliva di mare). Balls of fibrous material from its foliage, known as egagropili or Neptune balls, wash up to nearby shorelines.

The Posidonia has a very high carbon absorption capacity, being able to soak up 15 times more carbon dioxide every year than a similar sized piece of the Amazon rainforest.

Morphology

Posidonia oceanica has roots (which mainly serve to anchor the plant to the substrate), rhizome and tapeform leaves.

The rhizomes, up to 1 cm thick, grow both horizontally (plagiotropic rhizomes), and vertically (orthotropic rhizomes). The former, thanks to the presence at the bottom of lignited roots up to 15 cm long, anchor the plant to the substrate. The latter, which increase height, have the function of combatting sanding due to continuous sedimentation. 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. In this way, posidonias colonise an environment that algae could hardly occupy due to the lack of roots.

The leaves arise from orthotropic rhizomes, are cyntiform and bright green in colour that turns brown over time. They can reach a length of approximately 1.5 metres high. On average they have a width of 1 cm and have 13 to 17 parallel ribs. The apexes are rounded and are often lost by the action of waves and currents.

They are organised in bushes of 6 or 7 leaves, with the oldest on the outside and the youngest on the inside. The leaves are divided into three categories:

• Adult leaves, which have a lamina with photosynthetic function and a base separated from the foliar edge by a concave structure called "ligula";
• Intermediate leaves, which have no basis;
• Young leaves, which normally have a length of less than 50 mm. In autumn the plant loses the outermost adult leaves, which become brown and are photosynthetically inactive. During the winter, new leaves are produced.

Posidonia oceanica - Wikipedia