This is, along with Common Milkweed, a plant that I recall from my childhood. Looking way back, I recall one summer afternoon in the 1940's, when a young playmate's older brother—probably all of six-years old—confidently identified this yellow flowered plant as "sauerkraut." I'm sure I didn't know what sauerkraut was, but I took a piece of stem to chew and, while it wasn't sauerkraut (as I would learn later) I did find that this lawn weed had a pleasantly tart taste. So on those long-ago, lazy summer afternoons of my boyhood when I wanted a sour chew, I turned to a stem or two from the "sauerkraut plant." And still, when I come across it every so often, I'll sometimes end up with a wad in my cheek, just for old times sake!
Why is Sour Grass sour, you ask? Well, it is the crystals of oxalic acid found in the stems that make a "wad" pleasantly tart. (Jack-in-the-Pulpit, from a different family, also carries oxalic acid crystals in its leaves. I don't recommend chewing any of these lilies, of course!)
Fortunately, for a curious little boy—and a still-curious old man—a small, occasional chew of a salty and refreshing stem is reportedly not hazardous. Oxalic acid, as a regular part of ones diet, however, can lead to nutritional deficiencies and is considered to be toxic. One popular household scouring powder uses oxalic acid as an ingredient to aid in cutting through grease!
An immigrant from Europe, Oxalis stricta is commonly seen along the edges of fields and lawns in North America. (Depending on your locale you might know this lily as African Wood-sorrel, Bermuda Buttercup, Bermuda Sorrel, Buttercup Oxalis, Cape Sorrel, English Weed, Goat's-foot, Sourgrass, Soursob, or Yellow Oxalis.) The botanical prefix, Oxalis, in Latin—from Greek, oxys—and the common name, sorrel—from Old French, surele—are the words for "sour or bitter" in these languages.
The fruit stands upright, thus the scientific suffix, stricta, for "upright growth." They remind me of an ear of corn (maize).
(Sour Grass has a native relative, Violet Wood Sorrel (Oxalis violacea), that sports the same three-lobed "shamrock" foliage and also has a mild acidic taste. As you can see if you hover over the link, it presents a subtle violet and green blossom instead of the brilliant yellow flower of Oxalis stricta.)
As I hope is apparent from the images, this import to eastern North America from across the Atlantic is quite lovely up close. And although not appreciated by those desiring a pristine, weed-free lawn, it does offer a pretty yellow lily for our consideration, as well as a refreshing chew for browsing "boys"—young and old!