Mastocarpus stellatus (Stackhouse) Guiry

Also known as Gigartina stellata, Gigartina mammilosa and Petrocelis cruenta.
Common names: Clúimhín Cait (Irish); False Irish Moss, False Carragheen or Carrageen Moss (Eng.).
Description: Cartilaginous, purplish brown fronds, often in dense tufts, arising from a discoid holdfast, to 200 mm high. Narrow compressed stipe expands into strap-like blade, usually inrolled (above) to form a channel, with thickened margins. Repeatedly dichotomously branched, axils acute. Upper part of frond with papillae to 10 mm or more long on surfaces and margins on female plants. Male plants lack papillae but are generally rare. The tetrasporophyte is a purplish-black crust Petrocelis-phase, above right.
Habitat: On rocks in lower intertidal, often in large continuous mats, widespread and abundant.
Usage: In Ireland, collected more or less interchangeably with Chondrus crispus for use as Carrageen or Irish Moss

Link: AlgaeBase

Species list