The tetrasporangial phase forms much-branched, brownish-red tufts of fine filaments growing in small clumps with a width of 2.5 cm (1 in) and resembling cotton wool.

[4] The red colour of this species comes from the presence of the pigments phycoerythrin and phycocyanin which mask the chlorophyll a, beta-Carotene and various xanthophylls which are also present.

It was introduced into the northeastern Atlantic Ocean in the late nineteenth century, possibly arriving on the hull of a ship or among shellfish.

It is now present from Iceland and northern Norway southward to Portugal, as well as in the Canary Islands, Algeria, Tunisia and the Adriatic Sea.

[6] It grows in the low intertidal zone and to depths of about 8 m (26 ft) and can be abundant in lagoon-like areas on the lower shore.