Oxalis is from the Greek oxys acid referring to the sour taste of the leaves. Usually herbs with leaves alternate, compound with 3 leaflets which often fold back at night (pulvinate), apex of leaflets usually bilobed. Flowers 5-merous, petals usually yellow, stamens very shortly fused at the base. Carpels 5, ovary apocarpous to syncarpous, styles free; fruit usually a capsule.