Thongweed by Paul Taylor


Scientific name: Himanthalia elongata
One of the longest seaweeds native to the UK, thongweed helps create a beautiful underwater forest to rival that of any on the land!

Species information


2m long.

Conservation status


When to see

February - November.


This common brown seaweed, grows up to 2m long and has two distinct stages. It starts off as a tiny olive-green button attached to the rock, before long strap-like reproductive fronds grow rapidly between February and May.

How to identify

Button or mushroom like projections appear up to 2cm wide, from which long, thin, green-brown straps grow for up to 2m, branching into two as they go.


All coasts of Britain and Ireland, except for south east England.

Did you know?

This species lives for 2-3 years and only reproduces once before dying!

How people can help

Do not remove live, growing seaweed, particularly from Marine Conservation Areas. Always follow the Seashore Code when rockpooling, be careful to leave everything as you found it - replace any rocks you turn over, put back any crabs or fish and ensure not to scrape anything off its rocky home. If you want to learn more about our rockpool life, Wildlife Trusts around the UK run rockpool safaris and offer Shoresearch training - teaching you to survey your local rocky shore. The data collected is then used to protect our coasts and seas through better management or through the designation of Marine Protected Areas.