Scientific name: Cystoseira tamariscifolia
A bushy brown seaweed that appears bright blue underwater.
StatisticsGrows to 60cm tall
When to seeSpring and summer
AboutA 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 identifyA bushy seaweed with a tough main stem and small, spiky looking branchlets. When seen underwater, the blue and purple colouring gives it away.
DistributionThis 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 helpSeaweeds 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.