Easily recognized by their trios of heart-shaped leaflets, the Wood Sorrels (Oxalis spp.) pack a sour punch enjoyed by just about everyone to whom I introduce these plants. According to Go Botany, of the seven species of Oxalis who grow in New England, four have yellow flowers (O. corniculata, O. dillenii, O. florida, and O. stricta) and three have white, pink, or purple flowers (O. intermedia, O. montana, and O. violacea). The species I usually see growing as weeds in flower beds and gardens have yellow flowers.
Unlike Clovers (Trifolium spp.) who often have round or oval leaflets-of-three, the leaves of the Wood Sorrels are uniquely divided into three heart-shaped leaflets. Notice how each leaflet is creased like a paper heart and may fold in half during the heat of the day. The leaves, flowers, and young fruits are all edible, with the latter having a pleasant sour crunch. The leaves are thin, so be sure to sample a few at once to be sure you get enough to detect their flavor.
In many foraging books, Wood Sorrel accounts are brief, but experienced forager John Kallas allocated 14 pages of his book Edible Wild Plants (2010) to this wild food and included numerous full-color photographs, handy preparation tips, and recipes for Wood Sorrel soup, sauce, and dessert topping. Angelyn Whitmeyer (Identify that Plant) recently published a post and video showcasing Oxalis stricta, the Common Yellow Wood Sorrel. (To view the following images in full-size, click here.)