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Sea lettuce

life science Maturity 11-13 Next article →

Sea lettuce is a group of green algae known as the genus Ulva. These living things grow along coasts in oceans all over the world. One type is called Ulva lactuca, which means "lettuce" in Latin. Some people also call similar types green nori. These algae are important because many animals eat them. For example, manatees and sea hares like to eat sea lettuce.

Tufts of gutweed in Gullmarsfjorden at Sämstad 1
Tufts of gutweed in Gullmarsfjorden at Sämstad 1

Each plant has a special way it works to stay in place. They use a small disc called a holdfast to attach to things. The main body is a flat, leaf-like part called a thallus. This thallus can be light green or dark green in color. In sheltered areas where the water is calm, the blades can grow very large. One single blade can grow to be more than 400 mm long.

Humans have eaten sea lettuce for a very long time. In places like China and Japan, it is known as aosa. People in Scandinavia, Great Britain, and Ireland also eat it. You can eat it raw in salads or cook it in soups. It is a good food because it has protein and fiber. It also has vitamins and minerals like iron. Some people even chop it and mix it into bread dough.

There are many different species within the Ulva genus. Scientists have named many of them over the years. For example, Ulva intestinalis was named by Linnaeus in 1753. A new species called Ulva paschima was found in India in 2014. In 2022, researchers found ten new species in New Caledonia. These included names like Ulva arbuscula and Ulva finissima.

Sometimes, sea lettuce can cause a big problem on beaches. In August 2009, huge amounts of it washed up in Brittany, France. As the leaves rot, they make a gas called hydrogen sulfide. This gas is toxic and can be very dangerous to breathe. One horse rider lost consciousness and his horse died from the fumes. Experts say this might happen when chemicals from farms wash into the sea.

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