I'm assuming you're referring to the common Sheep Sorrel (Rumex acetosella).. ? Sheep sorrel contains vitamins A, B complex, C, D, E, and K, as well as anthraquinones, glycosides and oxalates.
For those who may not be aware: It contains oxalic acid (why it's so sour) which is toxic in large and repeated doses (herbal vinegar extraction is a form of medicinal tincture). It binds to and can inhibit calcium absorbtion, but the National Institutes of Health say the "interactions probably have little or no nutritional consequence" if you eat a variety of foods. Matt Wood, in "The Earthwise Herbal" says do not use sheep sorrel longer than three weeks without stopping for a week.