Phylum: Ochrophyta   Family: Fucaceae

Ascophyllum nodosum (Linnaeus) Le Jolis, 1863

Egg Wrack; Knotted Wrack

A common species of the middle shore. It has a narrow frond with a midrib, and air-bladders that are egg-shaped; these are produced annually in mature specimens. An important refuge for other plants and animals

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