The common yellow woodsorrel (Oxalis stricta) belongs to Oxalidaceae (the Wood sorrel family). It is a perennial herb that is native to North America. In Japan, it was found in Seika-cho, Kyoto Prefecture in 1962, and occasionally occurs on roadsides west of the northern Kanto region. The stems grows straight and up 10-25 cm in height. The leaves are divided into three heart-shaped leaflets that can grow up to 2 cm wide. These leaves curl up at night, and open in the day to perform photosynthesis. The small yellow flowers bloom from July to October. The whole plant is covered with white fulffs. After flowering, the fruit stalks droop, and square fruits bear.