Red sorrel is a very common herb. It can be used as a spice raw or cooked. It is best to use when its leaves are green. If the leaves are red in color, this is a sign that it contains a high amount of oxalic acid. It blooms from May to the beginning of August.
From Wikipedia: “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.”
Distribution and habitat:
“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. The American copper or small copper butterfly depends on it for food.”
“A perennial herb that has a slender and reddish upright stem that is branched at the top, reaching a height of 18 inches (0.5 meters). The arrow-shaped leaves are small, slightly longer than 1 inch (3 cm), and smooth with a pair of horizontal lobes at the base. It blooms during March to November, when yellowish-green (male) or reddish (female) flowers develop on separate plants at the apex of the stem, which develop into the red fruits (achenes).
Rumex acetosella is widely considered to be a hard-to-control noxious weed due to its spreading rhizome. Blueberry farmers are familiar with the weed because it thrives in the same conditions under which blueberries are cultivated.”
“There are several uses of sheep sorrel in the preparation of food including a garnish, a tart flavoring agent, a salad green, and a curdling agent for milk in cheese-making. The leaves have a lemony, tangy or nicely tart flavor. It is also known as sheep shower in parts of the country and there is a recipe for sheep shower wine online.”
“The oldest fossil record of red sorrel comes from the Boreal/Atlantic and was found in 1931 near Moosburg (Baden-Württemberg, Germany). The oldest literary mention is by Johann Bauhin in the year 1592.*”
Note (italics): * = Translation from a German Wikipedia entry