Marine plants

Credits: Seaweeds - Paul Naylor/

Plants don’t just grow on land – you can discover all sorts of fascinating plants and algae in the sea too. Seaweeds make their own food from sunlight energy, carbon and water just like plants that grow on land. Seaweeds can grow very big without needing woody trunks to support their structure.

Brown seaweeds, called kelps, can grow as big as trees and form underwater kelp forests - a special habitat for all sorts of other marine creatures. Marine plant life is restricted to the shallower areas of our seas as plants need light to survive. In the deeper parts of the oceans you will find only animals. Some of these animals, like sponges and corals, look very much like plants and are rooted to one spot. Most marine ‘plants’ are actually algae, including all of the seaweeds we find along the shore.


Did you know?

Carrageen, a seaweed extract, is commonly used in toothpaste and as a thickening additive in ice creams, puddings and milkshakes. Look for ‘carrageen’, ‘carrageenan’ or ‘E407’ on the ingredients list.

Five marine plants to look out for

Wracks: Brown seaweeds that cover many rocky shores. These are the seaweeds that make the rocks so slippery! There are several species. The bladder wrack has air bladders about the size of peas which ‘pop’ when you stand on them.

Sea lettuce: Thin, bright-green sheets of this species can be found in rock pools. In some parts of the world sea lettuce is eaten and is a valuable source of minerals.

Thongweed: An unmistakable seaweed with up to 2 metre long strap-like fronds in summer. All that remains in winter are the tiny ‘button mushrooms’ from which the fronds grow each summer.

Kelps: These are only revealed at the low water of spring tides. They mainly grow below the low water mark on rocky shores. There are several species of kelps and they form a rich habitat for other marine wildlife such as crabs and barnacles.

Eel grass: This is a flowering plant not an alga. Underwater forests of eelgrass support animals including cuttlefish, pipefish and sea hares and areas of eel grass exposed at low tide attract brent geese in winter which feed on its leaves.