Bright green grass under the ocean being pushed by currents
Posidonia oceanica

Neptune grass

Family: Posidoniaceae
Other common names: Posidònia (Catalan), 海神草 (Chinese), posidonie mořská (Czech), neptunusgras (Dutch), posidonie de méditerranée (French), posidonia mediterranea (Italian), Посидония океанская (Russian), deniz eriştesi (Turkish)
IUCN Red List status: Least Concern

Found only in the Mediterranean, neptune grass is a secret weapon in the battle against climate change.

This remarkable marine seagrass absorbs more carbon dioxide than an equivalent area of the Amazon rainforest.

Dense balls of dead neptune grass leaves are formed by ocean currents and can help trap plastics, removing them from the ocean when they wash up on the shore.

In 2006, a colony of neptune grass stretching over 8km and thought to be over 100,000 years old, was found off the coast of Ibiza. It is thought to be both the oldest and largest living organism on Earth.

Neptune grass forms larges undersea meadows in the sands of the Mediterranean Sea, from its shallow waters to around 40m deep. Specialised stems stretch into the sand and form a thick mat of roots that anchor the plant, while bright green ribbon-like leaves grow upwards to around 1.5m long and 10mm wide. Neptune grass produces small green flowers which develop into free-floating fruit commonly referred to as 'sea olives'.

Read the scientific profile on neptune grass

Food and drink

Neptune grass meadows provide grazing grounds for a variety of ocean life, including fish, urchins and turtles.

Materials and fuels

The dead leaf balls are occasionally used as compost.

In the past, dead leaves were used for animal bedding and insulation for housing.

  • Both the common and scientific name for neptune grass (Posidonia oceanica) come from classical gods of the sea. Poseidon is the Greek god of the sea, and Neptune is his Roman counterpart.

  • Neptune grass meadows provide an important habitat for marine life. They provide shelter for fish and are used as a nursery for their offspring.

  • Whilst neptune grass is exclusively found in the Mediterranean, all other members of the genus Posidonia are found off the southern coast of Australia.

A map showing where neptune grass is native to
Native: Albania, Algeria, Baleares, Corse, Cyprus, East Aegean Is., Egypt, France, Greece, Italy, Kriti, Libya, Morocco, Sardegna, Sicilia, Sinai, Spain, Tunisia, Turkey, Turkey-in-Europe, Yugoslavia

Temperate sea water in the Mediterranean Sea

Other plants

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The geographical areas mentioned on this page follow the World Geographical Scheme for Recording Plant Distributions (WGSRPD) developed by Biodiversity Information Standards (TDWG).