Sheep sorrel is, not surprisingly, a member of the sorrel family. It is also known as sheep's sorrel, red sorrel, sour weed, and field sorrel. The term, “Sorrel” comes from the Old French surele, which came from the Germanic sur which meant, “sour.” The “red” description coms from its red tinted stems and reddish-maroon flowers.
Like other sorrels, sheep sorrel contains oxalates. Many foods contain oxalic acid and it is fine in moderate amounts. A balanced diet and plenty of liquids flushes out excess oxalic acid. It is just when foods high in oxalic acid are consumed in large amounts that it becomes an issue. Straight oxalic acid is used commercially to remove rust from car radiators and antifreeze (ethylene glycol) is toxic primarily because it is converted to oxalate.
On the plus side, because of its high vitamin C content, sorrel has been used to prevent scurvy and the Sloan-Kettering Cancer Center reported that sheep sorrel increases muscular activity and fluid secretion in the intestines, preventing constipation.