Phylum: Ochrophyta   Family: Desmarestiaceae

Desmarestia ligulata (Stackhouse) J.V. Lamouroux, 1813

Desmarest's Flattened Weed; Flattened Acid Kelp

A tall species, with opposite, flattened branches which can be replicated several time. Found in the lower intertidal and subtidal. It has a high acid content and causes specimens to quickly break down, hence the common name of Acid Kelp. Often, the first sign of its presence is on the strand line where it bleaches quickly

References: 
Bunker, Brodie, Maggs & Bunker (2017) - Seaweeds of Britain and Ireland