Yellow wood sorrel is an herbaceous annual or perennial with taproots when young, developing rhizomes with age. Flowers in unevenly branched panicles on long stems, with 5 yellow, rounded petals. Blooms May–October. Leaves alternate, trifoliate (like clover), the leaflets heart-shaped, light to dark green or copper to purple, often recurved, sometimes with grayish hairs. At the end of each day, the leaflets droop or fold downward, parallel to the stem; they spread again the next morning. Fruit an upright, pointed capsule to about 1 inch long.
Similar species: There are 5 species of Oxalis in Missouri. One is violet wood sorrel, with pink or violet flowers. The other 4 all have yellow flowers. Of these, O. stricta is the tallest, most common, and the only one with flowers in panicles (a central flower flanked by a pair of branches bearing 2 or more flowers). The rest have the flower stalks umbellate (arising from the same point at the tip of a stem).
Height: 4 to 20 inches, occasionally to 3 feet.
Scattered statewide. This native plant occurs throughout North America and has been introduced widely in the Old World.
Habitat and Conservation
Found nearly everywhere. Occurs in bottomland and upland forests, savannas, upland prairies, glades, banks of streams and rivers, pastures, fields, gardens, railroads, roadsides, and other disturbed areas. Various species of oxalis are hosts in the complex life cycles of rusts that afflict corn, sorghum, and other crop grasses.
This plant is both garden weed and wild edible. It has a pleasant sour taste, which is why some people call it sourgrass or lemon clover. Nibble on it as you work in your garden, or add it to salads. Note that, like spinach and rhubarb, the oxalic acid in the plant makes it toxic if eaten in very large quantities.
There are several species of wood sorrels that are often sold as shamrocks. Purple-leaf shamrock or false shamrock (Oxalis triangularis), a South American species, is a popular houseplant. Another wood sorrel, called iron cross plant, pink shamrock, or four-leaf clover, is a Mexican species of (O. deppei, also called O. tetraphylla). It is often sold by florists as a kind of four-leaf clover. You can easily distinguish wood sorrels from clovers by the flower form.
Like other weedy plants, yellow wood sorrel colonizes disturbed soils and begins the revegetation process. A host of animals, ranging from insects to birds to rabbits and deer, eat this plant. Bobwhite, sparrows, and other birds eat the seeds. Many insects visit the flowers for pollen and nectar.