Rhodochorton purpureum (Lightfoot) Rosenvinge

Also known as Audouinella purpurea (Lightfoot) Woelkerling
Description: Plants forming matted purplish-red tufts or a thin turf of sparingly branched, erect filaments, 5-10 mm long. Cells 3-4 times as long as broad. Cells with a single reticulate plastid without pyrenoids, later fragmented. Reproducing by tetrasporangia in repeatedly branched clusters, November to February. Monosporangia absent.
Habitat: On rock or epiphytic (especially on Laminaria hyperborea stipes), upper infralittoral to subtidal, often in caves and shady crevices, and growing under Fucus spiralis on sheltered shores. Widely distributed, common.

Similar species: While Rhodochorton purpureum forms turfs in the upper indtertidal or layers on the surface of mud in calm water Rhodothamniella floridula forms more extensive turfs binding sand. Microscopic examination for the absence of pyrenoids is required to be certain of the identity of Rhodochorton purpureum.
Key characteristics: Turf-forming habit and association with upper intertidal or caves, or Laminaria hyperboreastipes, but not binding sand. Absence of monosporangia.

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