information on the biology of species and the ecology of habitats found around the coasts and seas of the British Isles

False Irish moss (Mastocarpus stellatus)

Distribution data supplied by the Ocean Biogeographic Information System (OBIS). To interrogate UK data visit the NBN Atlas.
Only coastal and marine records shown



A small red alga (up to 17 cm in length), the fronds are channelled with a thickened edge and widen from a narrow stipe with disc-like holdfast. The channelling is often slight and is most noticeable at the base of the frond. Mature plants have conspicuous growths of short, shout papillae (reproductive bodies) on the fronds. The plant is dark reddish-brown to purple in colour and may be bleached. The common name false Irish moss is used as it may be confused with Chondrus crispus (Irish moss). The main features separating the two species being the channelled frond and appearance of reproductive bodies on mature plants.

Recorded distribution in Britain and Ireland

Occurs all around the British Isles but is abundant mainly on western coasts.

Global distribution



This alga is found on rocky shores, particularly in very exposed areas where it grows amongst barnacles and mussels, on less exposed shores it is often abundant under fucoids. It mainly inhabits the lower shore and rockpools, but can be found in the shallow sublittoral and occasionally deeper waters.

Depth range


Identifying features

  • Up to 17 cm in length.
  • Channelled fronds with thickened edge widen from a narrow stipe.
  • Disc like holdfast.
  • Darkish reddish-brown to purple in colour.

Additional information

May be collected with Chondrus crispus as a source of 'carrageen', which is used to make soups and jellies, and also as a remedy for respiratory disorders in Ireland ('Carrageen' is a hot water extract of red algae).

Listed by

- none -

Further information sources

Search on:


  1. Dickinson, C.I., 1963. British seaweeds. London & Frome: Butler & Tanner Ltd.

  2. Fish, J.D. & Fish, S., 1996. A student's guide to the seashore. Cambridge: Cambridge University Press.

  3. Hardy, F.G. & Guiry, M.D., 2003. A check-list and atlas of the seaweeds of Britain and Ireland. London: British Phycological Society

  4. Howson, C.M. & Picton, B.E., 1997. The species directory of the marine fauna and flora of the British Isles and surrounding seas. Belfast: Ulster Museum. [Ulster Museum publication, no. 276.]

  5. JNCC (Joint Nature Conservation Committee), 1999. Marine Environment Resource Mapping And Information Database (MERMAID): Marine Nature Conservation Review Survey Database. [on-line]

  6. National Biodiversity Network (NBN) Atlas website. Available from:  Accessed 01 April 2017

  7. Picton, B.E. & Costello, M.J., 1998. BioMar biotope viewer: a guide to marine habitats, fauna and flora of Britain and Ireland. [CD-ROM] Environmental Sciences Unit, Trinity College, Dublin.


This review can be cited as:

Pizzolla, P.F 2008. Mastocarpus stellatus False Irish moss. In Tyler-Walters H. and Hiscock K. (eds) Marine Life Information Network: Biology and Sensitivity Key Information Reviews, [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 14-08-2018]. Available from:

Last Updated: 29/05/2008