Cladophora rupestris (Linnaeus) Kützing
Description: Thallus dark green (sometimes bluish), stiff, entwined, to 200 mm in length, composed of profusely, irregularly branched filaments apparent to the unaided eye. Attached by a rhizoidal holdfast. Persists throughout the year.
Habitat: on rock and in pools from mid-tide downwards, often growing under Fucus vesiculosusor Ascophyllum nodosum but such plants are generally smaller and darker. Common and widespread.
Key characteristics: dark green colour (other species of Cladophora and Spongomorpha aeruginosa are more grass-green in colour), stiff filaments.