[1] It has a strong and distinctive flavor, and is generally made into flat sheets and used to wrap rolls of sushi or onigiri (rice balls).

Nori—despite not being cultivated by humans until the 1600s—has been popular since the pre-modern era in Japan, having been used as currency, offerings at shrines, and food since the 700s.

The industry was rescued by knowledge derived from the work of British phycologist Kathleen Mary Drew-Baker, who had been researching the organism Porphyria umbilicalis that grew in the seas around Wales and was harvested for food (laverbread), as in Japan.

Her work was discovered by Japanese scientists who applied it to artificial methods of seeding and growing the nori, rescuing the industry.

Kathleen Baker was hailed in Japan as the "Mother of the Sea" and a statue was erected in her memory.

The word nori started to be used widely in the United States and the product (imported in dry form from Japan) became widely available at natural food stores and Asian-American grocery stores in the 1960s due to the macrobiotic movement [13] and in the 1970s with the increase of sushi bars and Japanese restaurants.

The most common (and least expensive) grades are imported from China, costing approximately six cents per sheet.

At the high end, ranging up to 90 cents per sheet, are "delicate shin-nori" (nori from the first of the year's several harvests) cultivated in the Ariake Sea, off the island of Kyushu in Japan.

[17] In Japan, more than 600 square kilometres (230 sq mi) of coastal waters are given to producing 350,000 tonnes (340,000 long tons) of nori, worth more than a billion dollars.

[18] Wild seaweed is still gathered to make nori, often found growing on rocks at the beach.

A related product, prepared from the unrelated green algae Monostroma and Enteromorpha, is called aonori (青海苔 literally blue/green nori) and it is used as an herb on everyday meals, such as okonomiyaki and yakisoba.

[21] By contrast, however, a 2017 review concluded that vitamin B12 may be destroyed during metabolism or is converted into inactive B12 analogs during drying and storage.