oxalis stricta

Oxalis stricta, called the common yellow woodsorrel (or simply yellow woodsorrel), common yellow oxalis, upright yellow-sorrel, lemon clover, or more ambiguously and informally 'sourgrass' or 'pickle plant', is a herbaceous plant native to North America, parts of Eurasia, and has a rare introduction in Britain. It tends to grow in woodlands, meadows, and in disturbed areas as both a perennial and annual. Erect when young, this plant later becomes decumbent as it lies down, and branches regularly. ...