It's Chinese cabbage.

Chinese cabbage is the algae body of Ulva pertusa, also known as sea spinach, sea lettuce, seaweed, moss vegetables and so on. The scientific name is Ulva. Chlorophyta, Ulva. Algae are bright green, solitary or clustered, and often have holes of different sizes. Chinese cabbage, green algae, polygonal cells, mononuclear cells, chloroplast sheets and a starch nucleus.

It is a membranous body composed of two layers of cells, with oval leaves and wavy edges, with a height of 1 ~ 3cm. The sessile base is a disk-shaped fixator, which is composed of many false root filaments extending downward between the two layers of cells at the base. Asexual reproduction and sexual reproduction, sporophyte and gametophyte alternate with each other. Living on rocks or bogs in the middle and low intertidal zone. China East China Sea and South China Sea are common, and can be eaten and used as bait.

Extended information

Introduction to knowledge of Chinese cabbage: Chinese cabbage is the algae body of Ulva pertusa, an algae plant of Ulva family. The algae body is bright green, solitary or clustered, with a height of 1-14 cm, and the body often has holes of different sizes. The edible part of Chinese cabbage contains 47.8g of water, 11.2g of protein, .1g of fat, 4.3g of carbohydrate and crude fiber, and also contains various minerals and vitamins.

grows on rocks in the middle and low tide zone. It is distributed in Bohai Sea, Yellow Sea, East China Sea, and less in South China Sea. Contains a variety of minerals and vitamins.