Fat choy (Nostoc flagelliforme), also known as faat choy, fa cai, black moss, hair moss or hair weed is a terrestrial cyanobacterium (a type of photosyntheticbacteria) that is used as a vegetable in Chinese cuisine. When dried, the product has the appearance of black hair. For that reason, its name in Chinese means "hair vegetable." When soaked, this vegetable has a very soft texture which is like very fine vermicelli.
Fat choy grows on the ground in the Gobi Desert and the Qinghai Plateau. Over-harvesting on the Mongolian steppes has furthered erosion and desertification in those areas. The Chinese government has limited its harvesting, which has caused its price to increase. This may be one reason why some commercially available fat choy has been found to be adulterated with strands of a non-cellular starchy material, with other additives and dyes. Real fat choy is dark green in color, while the counterfeit fat choy appears black.
But, Paul Pui-Hay; Ling Cheng; Pui Kwan Chan; David Tai-Wai Lau; and Joyce Wing-Hin But (2002). "Nostoc flagelliforme and Faked Items Retailed in Hong Kong." Journal of Applied Phycology 14: 143-145.
Takenaka, H., Yamaguchi, Y., Sakaki, S., Watarai, K., Tanaka, N., Hori, M., Seki, H., M. Tsuchida, M., Yamada, A., Nishimori, T., and Morinaga, T. "Safety evaluation of Nostoc flagelliforme (nostocales, cyanophyceae) as a potential food". Food and Chemical Toxicology. 1998. Volume 36, Issue 12. Pages 1073-1077.