Answer: Aztecs

Spirulina, now sold as a health supplement with a wide range of purported (but clinically unproven) benefits, is a form of algae with a long history as a food stuff. Long before it was packaged into neat tablets and displayed on health food store shelves, it was eaten by the Aztecs and other Mesoamerican peoples.

The Aztecs harvested the algae from Lake Texcoco and formed it into dried cakes (called tecuitlatl) that were sold in markets alongside food stuffs more recognizable to a modern reader. After the 16th century, when the Aztecs drained the smaller surrounding lakes in order to develop agricultural land and expand their cities, the harvesting of Spirulina fell out of practice and the process and knowledge of the cakes practically vanished.

It was only because of chemical analysis of Spirulina in the mid 1960s, consumed as dried cakes (called dihe) by the totally separate culture of the Kanembu tribe in Africa, that researchers began searching for other cultures that did, or had done, the same.