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 be
(Wikipedia)