English: Sour grass; Sour trefoil; Shamrock; Violet wood-sorrel.
Region: United States, Rocky Mountains, Atlantic Ocean, Gulf of Mexico coasts, Eastern Canada.
Botany: perennial; open places, in damp woods, on stream banks, in moist prairies; emerges in early spring from an underground bulb, ± average 20 cm high; leaves three-part, heart-shaped; flowers violet.
Use: medicinal by Native Americans; edible flowers, leaves, stems, bulb; sour juice in salads; ornamental, groundcover.