Rainbow wrack

Rainbow wrack

Rainbow wrack ©Helen Earwicker

Rainbow wrack

Rainbow wrack ©Sarah Hodgson

Rainbow wrack

Rainbow wrack ©Julie Hatcher

Rainbow wrack

Scientific name: Cystoseira tamariscifolia
A bushy brown seaweed that appears bright blue underwater.

Species information


Grows to 60cm tall

Conservation status


When to see

Spring and summer


A distinctive and colourful seaweed, with a tough main stem from which a profusion of side branches and smaller fronds grow. The stem, also called a stipe, is often covered in sponges and other growth, especially near the base.

Because rainbow wrack grows in the intertidal zone, it is exposed to lots of sunlight and the bright colours tend to fade as the summer progresses. The colours are always most vivid in spring, but to enjoy the best effect look amongst the lowest branches, which remain shaded and keep their colour for longer.

How to identify

A bushy seaweed with a tough main stem and small, spiky looking branchlets. When seen underwater, the blue and purple colouring gives it away.


This colourful seaweed is more common in the south and west in the UK.

Did you know?

An alternative name for rainbow wrack is magic seaweed. At low tide, when left high and dry out of water, it appears to be brown, but when viewed underwater it turns bright shades of turquoise, indigo and violet. If you find a piece washed up and unattached on the beach, pop it into the nearest rockpool and watch it change colour!

How people can help

Seaweeds provide food and shelter for all kinds of shore creatures, so do not detach seaweed from the rocks or pull branches off, and avoid trampling through rockpools. Leave everything as you found it and always follow the Seashore Code to avoid damage to rocky shore species.

If you want to learn more about our rockpool life, Wildlife Trusts around the UK run rockpool safaris.