Yellow Wood Sorrel
Wood Sorrel family (Oxalidaceae)
Description: This native perennial plant is usually about 6" tall, but sometimes reaches 1' or a little more. There is a central stem that branches occasionally, creating a bushy effect on mature plants. It is often covered with scattered white hairs. The alternate trifoliate leaves have fairly long petioles, and are about ¾" across when fully open. Depending on environmental conditions, they are light green, green, or reddish green, and fold up at night. Occasionally, they fold up in response to intense sunlight during midday.
Floppy umbels of yellow flowers emerge from the leaf axils on long, slightly hairy stalks. Each bell-shaped flower is about ½" across when fully open, and has 5 petals that flare outward. There are fine lines toward the throat of the flower, which is subtended by 5 green triangular sepals. Sometimes, the throat of the flower is slightly red. Like the leaves, the flowers close-up at night. There is little or no floral scent. The blooming period peaks during late spring or early summer, but continues intermittently until the fall. Plants often become dormant during the hot dry spells of mid- to late summer. The root system consists of a slender branching taproot with numerous secondary roots. This plant spreads by means of mechanical ejection of the seeds from the slightly hairy elongated seed capsules; each capsule splits into 5 sections.
Cultivation: The preference is full or partial sun, and moist to slightly dry conditions. Growth is best in a rich loamy soil, although poor soil containing clay, gravel, or sand is tolerated. Yellow Wood Sorrel is a very robust little plant and will spread, if it is given half a chance, particularly in open, disturbed situations. It doesn't compete well against taller plants, however. Foliar disease doesn't appear to affect this plant significantly.
Range & Habitat: Yellow Wood Sorrel is a common plant that occurs in every county of Illinois (see Distribution Map). Habitats include mesic black soil prairies, openings in woodlands, savannas, limestone glades, pastures, lawns and gardens, powerline clearances, edges of paths and driveways, and miscellaneous waste areas. This plant is more common in degraded habitats.
Faunal Associations: Flower visitors include small bees, Syrphid flies, bee flies, small butterflies, and skippers. Among these insects, bees are probably the most important pollinators, including such species as Ceratina dupla dupla (Little Carpenter Bee), Calliopsis andreniformis (Andrenid Dagger Bee), and Melissodes bimaculata bimaculata (Two-Spotted Miner Bee). The Syrphid flies feed on pollen and are non-pollinating. Several species of songbirds and upland gamebirds eat the seeds, including the Bobwhite, Mourning Dove, Horned Lark, Field Sparrow, Grasshopper Sparrow, Savannah Sparrow, and Slate-Colored Junco (winter only). The Cottontail Rabbit and White-Tailed Deer eat this plant occasionally, even though the leaves are slightly toxic from oxalic acid.
Photographic Location: The photographs were taken on the grounds of the webmaster's apartment complex in Urbana, Illinois.
Comments: This little plant is cute-looking when covered with yellow flowers, but devalued because of its ubiquitousness. The leaves can be added to salads in small amounts they have a slightly sour taste. Some authorities recognize another species of wood sorrel, Oxalis dillenii, which also has yellow flowers and is very similar to Oxalis stricta. The former species is supposed to have more erect pedicels, rhizomes, and other slightly different traits that distinguish it from Oxalis stricta. However, it seems more likely that these are merely variations of the same species.