Have you ever had French sorrel? It's one of those greens you might find in your salad at an uptown restaurant, where it was probably flown in from a small farm in northern California, certified organic and $10 a pound. If you've ever overpaid for a gourmet salad, you may be intrigued to know (or resentful, depending on your disposition) that you can almost without a doubt find essentially the same plant growing within a three-block radius of your house, if not in your very own yard.
It is called Rumex crispus, also known as yellow dock, and it likes to grow in hard dry clay, cracks in the sidewalk and other such inhospitable places. The young leaves have exactly the same flavor as French sorrel — a combination of lemon zest and spinach — also known as Rumex scutatus. The two share the same name because genetically they are almost the same plant. It's just the one found in fancy restaurants and boutique food stores has been pampered and selected by gardeners to have bigger leaves that stay tender and succulent past the juvenile stage.
Yellow dock owes its ability to survive anywhere to its enormous woody taproot — the same feature that causes gardeners so much consternation when they try to remove it. The root inevitably breaks off 9 inches down when you try to pull it and then grows back from the depths three weeks later when you're not looking. It does, however, have the ability to unlock minerals from the subsoil that other plants can't access, which it stores in its leaves, making yellow dock orders of magnitude more nutritious than spinach — a reason, perhaps, to let a few grow.