Most plants in the oxalidaceae (wood sorrel) family have trifoliate leaves, the leaflets usually heart-shaped, attached at the point, and often folding up along the midvein during the night. Flowers are formed of a five-lobed calyx, five petals, ten stamens (five of which are sometimes infertile), and a compound pistil of five fused carpels. There is only one native UK species, oxalis acetosella, plus several naturalised varieties, or garden escapes.