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.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).