The Yellow sorrel (Oxalis corniculata) belongs to Oxalidaceae (the Wood sorrel family). It is a perennial herb that is distributed worldwidely, from temperate areas to tropical areas. It can be found usually in dry fields or roadsides. The stem is creeping on the ground and blooms yellow flowers from May to September. The stem and leaves contain oxalic acid, and have acid taste. It is also called "Zeni-migaki" (cion polisher) in Japan because it becomes beautiful when you polish coins with leaves and stems. In Taiwanese Chinese, it is called "酢漿草" and "酢漿草" (cu jiang cao).