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 colour.
The plant is native to Eurasia and the British Isles, but it has been introduced to most of the rest of the Northern Hemisphere. It is commonly found on acidic, sandy soils in heaths and grassland. 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. Livestock will graze on the plant, but it is not very nutritious and is toxic in large amounts because of oxalates.