Heh, I learned something new today! What we call wood sorrel is Oxalis acetosella. Thanks to Wikipedia, now I know that:

Oxalis ... is a large genus of flowering plants in the wood-sorrel family Oxalidaceae comprising about 570 species.

Many of the species are known as wood sorrels (sometimes written "woodsorrels" or "wood-sorrels") as they have an acidic taste reminiscent of the unrelated sorrel proper (Rumex acetosa).