Biodiversity & Conservation

False Irish moss - Mastocarpus stellatus

Mastocarpus stellatus

Image Francisco Arenas - The seaweed Mastocarpus stellatus. Image width ca 15 cm.
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Distribution map

Mastocarpus stellatus recorded (dark blue bullet) and expected (light blue bullet) distribution in Britain and Ireland (see below)

Why do the maps differ?

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Mastocarpus stellatus is not listed under any importance categories.

Taxonomy icon Taxonomy Taxon English term
Phylum Rhodophyta Red seaweeds
Class Florideophyceae
Authority (Stackhouse) Guiry
Recent synonyms Gigartina stellata
Map icon Recorded Distribution in Britain and Ireland Occurs all around the British Isles but is abundant mainly on western coasts.
Habitat information icon Habitat information 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.
Text page icon Description 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.
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 icon 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).

This review can be cited as follows:

Paolo Pizzolla 2008. Mastocarpus stellatus. False Irish moss. Marine Life Information Network: Biology and Sensitivity Key Information Sub-programme [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 28/11/2015]. Available from: <>