Flowers: terminal; solitary. Calyx: of five lanceolate sepals. Corolla: of five petals. Stamens: ten. Pistil: one; styles, five. Leaves: divided into three obcordate, smooth leaflets. Stem: slender; erect.
An odd thing about this pretty sorrel that greets us along the roadsides, is the difficulty it seems to have about deciding the matter of fertilization. The cleistogamous blossoms that it bears are naturally self-fertilized: while the showy flowers most cautiously prevent such a thing by being either dimorphous or trimorphous, - that is, they have stamens and pistils of two different lengths. The short pistils must receive the pollen from the short stamens in another blossom; and the long pistils, the pollen from the long stamens.
At night the plant folds together its leaves and sleeps. O. acetosella, Plate CV.