Laver was originally a Latin word. It was used by Pliny for an (unspecified) water plant, apparently as a synonym of Greek síon, which denoted variously the ‘water parsnip’, the ‘water pimpernel’, and the ‘watercress’. Both terms were taken over by English herbalists. William Turner, for instance, in his Herbal (1562), writes: ‘Sion otherwise called lauer is found in waters with a fat bushe ryght vp with brode leues.’ Then suddenly, at the beginning of the seventeenth century, we find laver being used for ‘seaweed’, and by the 1800s it had become established as a term for ‘edible seaweed’ (typically of the genus Porphyra): John Arbuthnot, in his Rules of Diet (1732), mentions ‘Laver, which is the Lactuca Marina or Sea-Lettuce’, and Christopher Anstey's Bath Guide (1766) reports the selling of it in the streets with the cry ‘Fine potted Laver, fresh Oysters, and Pies!’ It is clear that until comparatively recently the consumption of seaweed was common amongst coastal communities in all parts of the British Isles, but the Gaelic origin of alternative names for laver and other species, such as dulse and slawk, clearly suggest that it has always been more acceptable to the Celtic palate than to Anglo-Saxon ones, and in the twentieth century laver came to be very closely associated with Welsh cuisine. The main reason for its fame has no doubt been laverbread, a particular way the Welsh have with the seaweed. White Kennet, in Cowell's Interpreter (1701), reported on this strange dish with all the detachment of an anthropologist: ‘In Glamorganshire and some other parts of Wales, they make a sort of Food of a Sea plant, which seems to be the Oyster-green or Sea-liver-wort. This they call Laver-bread.’ In recent years, however, Welsh proselytism and an increased interest in British regional cuisine have gained a wider audience for laverbread—which is boiled laver mixed with oatmeal and fried in bacon fat, butter, etc.
In Cornwall, edible seaweed is known as blackbutter.