Rumex acetosella, commonly known as sheep's sorrel, red sorrel, sour weed and field sorrel, is a species of flowering plant in the buckwheat family Polygonaceae. The plant and its subspecies are common perennial weeds. It has green arrowhead-shaped leaves and red-tinted deeply ridged stems, and it sprouts from an aggressive and spreading rhizome. The flowers emerge from a tall, upright stem. Female flowers are maroon in color.