Species:

Note: The species grows in the upper subtidal and is most common at wave-exposed sites along the coast of Norway. It is normally 10-20 cm long and is uniseriate and unbranched, and has a conspicuous dark blue-green colour and large and often barrel-shaped cells (in middle part of thallus). The basal cell is 1-3 mm long. The cells above the basal cell have length to width ratios of 4-8, this relationship decreases towards the upper part of thallus (to l/w 1-2). Small specimens can be confused with C. linum.