Phylum: Ochrophyta   Family: Laminariaceae

Laminaria digitata  (Hudson) J.V. Lamouroux, 1813

Oarweed; Tangle

It forms large masses in the low-water zone. It has a smooth stipe with a fingered holdfast. Multiple broad fronds eminate from the stipe which can reach 2 metres in length

References: 
Fish & Fish (2011) - A Student's Guide to the Seashore;
Bunker, et al - Seaweeds of Britain and Ireland