Fat choy is an ingredient in some Chinese cuisine comprising a dried Nostoc bacterial colony. Nostoc colonies form a jelly-like substance to help them survive in the range of environments they live in. This dark green gel is then harvested (often illegally), dried, and cooked. The resulting product looks essentially like black hair. Even though it is the remnants of bacteria, it is considered a vegetable in Chinese cuisine, and its Chinese name fàcài literally means “hair vegetable”.
This vegetable has essentially no nutritional or medicinal value, but has nonetheless been eaten for centuries as a noodle substitute. It is traditionally eaten on Chinese New Year, as its name sounds like much like fācái, which means “get rich” and is part of a common New Year’s greeting.