Porphyra umbilicalis Kützing, 1843

Common names: Sleabhach, Sleabhcán, Sliucáin, Sleadaí (Irish); Laver, Tough Laver, Slack (English), Nori (generic English name derived from Japanese word for Porphyra and Pyropia)
Description: Variable in colour from brownish-purple to olive-yellow.  Membranous, one cell layer in thickness, to 130 mm long and 100 mm wide, irregularaly lobed and split from central holdfast. Appraring almost orbicular; often much pleated, and multiple baldes grouped together to appear like a rosette. SImilar to thick plastic sheeting to touch.
Habitat: Generally on mussels, sometimes on rock; mid-intertidal to splash zone, generally distributed, abundant, especially on exposed coasts in spring and summer.
Key characteristics: centrally attached fronds, lettuce-like appearance. May be a species-complex.
Usage: At Kilkee, Co. Clare, Ireland, it is gathered in spring for boiling with bacon where it is known as known as Slack, Sleabhac, or Sliucáin (John Williams, Kilkee, pers. comm.). In Wales, it and other species are used to make laverbread, which is also availble in tinned form. 

Species list