Phylum: Rhodophyta   Family: Sphaerococcaceae

Sphaerococcus coronopifolius   Stackhouse, 1797

Berry Wart Cress

A common subtidal species, growing on rock. Cartilaginous with broad flattened fronds

References: 
Dixon & Irvine (1997) - Seaweeds of the British Isles, Volume 1 Rhodophyta, Part 1 Introduction, Nemaliales, Gigartinales;
Bunker, Brodie, Maggs & Bunker (2017) - Seaweeds of Britain and Ireland