Sheep Sorrel (Rumex acetosella) is a species of sorrel bearing the common names sheep's sorrel, red sorrel, sour weed, and field sorrel. 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 rhizome. The flowers emerge from a tall, upright stem. Female flowers are maroon in color.
The plant is native to Eurasia but has been introduced to most of the rest of the northern hemisphere. In North America it is a common weed in fields, grasslands, and woodlands. It favors moist soil, so it thrives in floodplains and near marshes. It is often one of the first species to take hold in disturbed areas, such as abandoned mining sites, especially if the soil is acidic.