Phylum: Rhodophyta   Family: Rhodomelaceae

Laurencia obtusa  (Hudson) J.V. Lamouroux, 1813

Rounded Brittle Fern Weed

Epiphytic and epilithic in the inter-tidal and subtidal. Relatively common but easily confused with similar species

References: 
Maggs & Hommersand (1993) - Seaweeds of the British Isles, Volume 1 Rhodophyta, Part 3A Ceramiales;
Bunker, Brodie, Maggs & Bunker (2017) - Seaweeds of Britain and Ireland