Low herbs with an acid juice and alternate compound leaves, the 3 leaflets obcordate and drooping in the evening. Flowers very much the same in structure as in the preceding Order, but the fruit is a 5-celled pod, each cell opening in the middle of the back (loculicidal), and the valves persistent. Styles 5, separate. The only genus is
1. 0. Acetosel'la, L. (White Wood-Sorrel.) Scape 1-flowered. Petals white, with reddish veins. - Cold woods.
2. 0. corniculata, L. (Yellow W.) Annual, or perennial by running underground shoots. Stipules present. Peduncles 2-6-flowered, longer than the leaves. Petals yellow. Pod elongated, erect in fruit. - Rare.
Var. stricta, Sav. (0. stricta, L.), is less pubescent, has an erect stem, and is without stipules. - Common