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. Livestock will graze on the plant, but it is not very nutritious and contains oxalates which make the plant toxic if grazed in large amounts.
Rumex acetosella is a host plant for Lycaena phlaeas, also known as the American Copper or Small Copper butterfly.
Sheep's sorrel is widely considered to be a noxious weed, and one that is hard to control due to its spreading rhizome. Blueberry farmers are familiar with the weed, due to its ability to thrive in the same conditions under which blueberries are cultivated. It is commonly considered by farmers as an Indicator plant of the need for liming.
There are several uses of sheep sorrel in the preparation of food including a garnish, a tart favoring agent and a curdling agent for cheese. The leaves have a lemony, tangy or nicely tart flavor.
It has a number of purported uses and folk remedies that include treatment for inflammation, cancer treatment, diarrhea, scurvy and fever. A tea made from the stem and leaves can be made to act as a diuretic. It also has certain astringent properties and uses. Other historical uses include that of a vermifuge, as the plant allegedly contains compounds toxic to intestinal parasites (worms).
From the 1950s, the New South Wales Soil Conservation Service undertook an extensive program of rehabilitation of the vegetation of the Carruthers Peak–Mount Twynam area, which was in sore need of help after a century of grazing. They tried various methods using bitumen, wire netting and bales of straw, however none were very successful. However, Sheep Sorrel was present in the bales of straw, and in fact helped to hold the soil for recolonisation by the native vegetation.