Cystoseira baccata (S.G. Gmelin) P.C. Silva
Description: Thllus to 1 m long, usually solitary, attached by a thick, conical attachment disc. Axis simple or branched, up to a metre in length, flattened, about 1.0 x 0.4 cm in transverse section; apex smooth and surrounded during periods of active growth by incurved young laterals. Lateral branch systems distichous, alternate, radially symmetrical, profusely branched in a repeatedly pinnate fashion and bearing sparse, filiform, occasionally bifurcate appendages on the branches of higher orders; deciduous, leaving decurrent bases which give an irregular, zigzag outline to the axis. Cryptostomata absent. Air vesicles present in axes of branches of higher order, sometimes in chains; seasonal, particularly numerous in autumn. Receptacles 1-5 cm long, formed from axes of ultimate ramuli, irregularly nodose and bearing simple, filiform appendages.
Habitat: lower intertidal in large sandy pools or lagoons, mostly in persistent stands.
Distribution: S England, W Ireland north to W Scotland.
Key characteristics: Intercalary pea-sized air vesicles, sometimes in chains.