Growing up, we knew Sheep Sorrel simply as Sour Grass. We chewed on it for its tart, mouth puckering jolt of flavor. Now, we know it has a myriad of other uses. Sour Grass, or Sheep Sorrel, Rumex acetosella, is also sometimes called Red Sorrel or Field Sorrel. It is a member of the Buckwheat family and can quickly spread in an area it likes. It multiplies via rhizomes, so if there’s a place you don’t want it, dig it up, roots and all. After reading though, you may decide you would like to keep it, or locate it to a place where you can control it. We have it in our field, which is good and bad, but I like to keep a patch contained in my medicinals garden. I treat it like mint, in that I sink a barrier around it to keep it in. You can use landscape edging, an old patio sized planter with the bottom half cut off, or anything solid like that. I caution against using rocks or even garden center rocks that fit together, because those rhizomes WILL find the cracks and go through.
Sheep Sorrel is easily distinguished by its arrow shaped green leaves. The stalk has ridges that resembles celery and can be green or red, depending on their age and will have a cluster of spikes at the top bearing green or red seeds (again depending on the maturity). Sometimes it will be a fade from green to red on both the stalk and the seed head.
For Food: As I mentioned before, you can pick the stalk and chew it for its tart, zingy flavor, but sheep sorrel is also great in recipes. Use leaves or snipped stalks (think snipped chives) in salads, over poached eggs or in scrambled eggs (a special treat if you’re camping), in soups, pesto, as a lemony garnish for fish or chicken dishes, a garnish for sauteed asparagus, in place of spinach in spinach dip, add snipped stems into fried rice, use finely diced leaves with some parsley to herb soft cheeses… you get the idea. The possibilities are endless! It can also be used as a mordant in the fiber dying process, but that is a whole other discussion, lol.
For Medicine: The same compound that gives sheep sorrel its tart flavor, oxalic acid, also lends it to be medicinal.
As a Tea, it is anti-inflammatory, anti-microbial, and anti-parasitic making it a good treatment for colds and flu; to kill intestinal parasites; as a diuretic or periodic detox, an immune system booster, and to combat chronic inflammation which is known to the be at the root of many modern ailments. A week tea, prepared in distilled water can also be used in a neti pot in place of salt-water rinse for sinus infections. Use leaves fresh or dried. If using fresh, I prefer the decoction method of one cup of tightly packed leaves to one quart of boiling water. Place the leaves in a mason jar, pour boiling water over them, cap and leave until cooled. This makes a stronger tea and can be taken in 8 ounce servings once a day for colds and flu, as soon as you notice symptoms. For parasites, do the same for a course of 2 weeks. Dried leaves can be used similar to ordinary tea in the proportion of 1 heaping teaspoon to 8 ounces of boiling water and steep for up to 10 minutes.
As a Poultice, it is anti-inflammatory and anti-microbial making it a good treatment for cuts, burns and according to some, possibly even certain types of skin cancers. There has been a bit of research done on its cancer fighting ability, stemming from sheep sorrel’s traditional use as one of the ingredients in Essiac tonic, which was originally used by the Ojibwa tribe in Canada. If you’re interested in more about this, here is a good article that leads to a giant rabbit hole. 
Essiac Tea – History Recipes and Benefits
One important note: If you are prone to calcium oxalate kidney stones, consume sheep sorrel as tea or food sparingly. Oxalic acid and the tannins contained in sheep sorrel can be one of the compounds that certain people have issue with that form calcium oxalate kidney stones. (there are several types of kidney stones; calcium oxalate stones, uric acid stones, struvite and cystine so research what type your stones are).