Description:
Gametophyte narrow, compressed, two-edged, cartilaginous, scarlet fronds, main axes dark brownish-red, to 300 mm long. Branching abundant, distichous, subdichotomous or alternate, terminal branchlets acute, fringed with short marginal proliferations. Tetrasporophyte (formerly called Haematocelis fissurata) a thick crust with oily fissures, with which it is sometimes found.

Habitat:
Gametophyte on rock, rarely in lower intertidal (and then generally stunted) subtidal to ?? m., southern and western shores of Britain and Ireland, frequent. Not uncommon in drift. Tetrasporophyte known only in subtidal to ?? m.

Similar species: Plocamium cartilagineum is a lighter red colour, is more regularly branched with secund branchlets and is more common in the intertidal.