Porphyra umbilicalis, commonly called "laver", is a species of seaweed in the genus Porphyra.

It is smooth in texture and forms delicate, sheetlike thalli, reaching 25 centimetres (10 in) long[1] and often clinging to rocks.

[2] Porphyra is classified as red algae; it tends to be a brownish colour, but boils down to a dark green pulp when prepared.

It is unusual amongst seaweeds because the fronds are only one cell thick.

[3][4] It is commonly found around the west coast of Great Britain and east coast of Ireland along the Irish Sea, where it is also known as "sleabhac" or "slake".