Cystoseira tamariscifolia (Stackhouse) Papenfuss
Description: Thalli solitary, up to 1 metre long, bushy, with a pronounced greenish or bluish iridescence when submerged (above) or wet; attached by a conical disc. Axis cylindrical, up to 60 cm long, usually branched and with an inconspicuous apex. Lateral branch systems arising in spiral sequence, up to 60 cm long, profusely branched in a repeatedly pinnate fashion, showing radial symmetry and bearing simple or bifid spine-like appendages: deciduous, leaving prominent scars or stumps. Cryptostomata present on branches and appendages. Air vesicles often present in axes of ultimate ramuli; ovoid, up to 5 mm long. Receptacles 1-2 cm long, formed from terminal regions of ultimate ramuli and the branches which bear them; irregularly nodose and bearing short simple spine-like appendages; simple or branched, often distal to an aerocyst.
Habitat: Found in large intertidal rock pools and lagoons, where it can be a colourful addition to the flora; also in shallow subtidal.
Distribution: Southern and western shores of Britain and Ireland, north to the Hebridies in Scotland; Atlantic France and Spain south to North Africa; Western Mediterranean.
Photographs © M.D. Guiry