Oxalis europaea Jord.
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 an 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. It is not to be confused with similar plants which are also often referred to as "yellow woodsorrel".
Commonly considered a weed of gardens, fields, and lawns, it grows in full sun or shade. The alternate leaves of this plant are divided into three heart-shaped leaflets (a typical trait of other species of Oxalis) that can grow up to 2 cm wide. These leaves curl up at night (exhibiting nyctinasty), and open in the day to perform photosynthesis. The mature seed capsules open explosively when disturbed (a very similar trait to that of the mature seed capsules or fruits of plants found in the genus Impatiens) and can disperse seeds up to 4 meters (about 13 feet) away. The flowers of the plant are hermaphroditic, blooming from July to October.
O. stricta generally requires dry or moist, alkaline soils, preferring sandy and loamy dirt to grow in. It requires well-drained soil and can grow in nutritionally poor grounds. It does not do well in shade.
The leaves and flowers of the plant are sometimes added to salads for decoration and flavoring. These can also be chewed raw (along with other parts of the plant, but not the root) as a thirst quencher. The green pods are pleasant raw, having a juicy crisp texture and a tartness similar to rhubarb in flavor.
The juices of the plant have been extracted from its greens as a substitute to common vinegar.
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