When we say “vegetable”, the first thing that comes to mind is an edible plant that grows on land. But there are vegetables that grow in water.

Water spinach (one variety is called “morning glory” in Southeast Asia) grows on swamps.
Seaweeds grow in the sea where they are harvested. Edible seaweeds are sea vegetables. They are marine algae that range in color from red to brown to green.
Umi-budō
In Japanese cuisine, seaweeds are eaten fresh — often, raw — or dried. The most well-known seaweed eaten fresh is the sea grape (above). It is especially popular in Okinawa where it is known as umi-budō.
What does umi-budō taste like? Briny. When you pop a piece into your mouth and chew it, the tiny spheres explode and the briny water is released inside your mouth.
Nori
Among the dried seaweeds used in Japanese cooking, the most widely-known is nori.

Dried sheets of nori are used to make sushi. Thinly sliced nori is used as garnish for an array of dishes including soups.
Nori does not need to be rehydrated. It is ready to eat straight from its packaging.
Wakame
If you’ve wondered what the green vegetable in your miso soup is, it’s called wakame.

Wakame is sold dried. To use it, place the required amount in a bowl, pour in hot water and leave to rehydrate. The seaweed will more than double in bulk.
Kombu

Kombu is a tough and fibrous kelp. It is one of the two main ingredients for making dashi.
But kombu isn’t just for making dashi. You can use it as a vegetable in salads, stir fries and other dishes.
Like wakame, you need to soak kombu in hot water to soften before using as a vegetable ingredient. Note, however, that because kombu is tougher, it requires a longer cooking time than wakame.
Hijiki

Hijiki, the black strands in the mixture in the photo above, is used in salads, stews and soups. Rehydrate in hot water before adding to salads. Boil or simmer directly in sauce or broth to use in stews and soups.
Vitamins and minerals in seaweeds
Seaweeds are virtually fat-free, low in calories and rich in many vitamins and minerals. They are a great source of iodine, calcium and magnesium, and Vitamin B12, among others.