Field madder (Sherardia arvensis) is a common weed found in grassland throughout Europe and Western Asia. It is easily identified: whorls of narrow pointed leaves are arranged at intervals along the brittle, green stem. Flowers are in clusters surrounded by green bracts.

The term madder refers to its use as a dye. It is sometimes called blue madder, though the flowers are pink and the dye produced from the roots is rosy-red. It is considered to be inferior as a dye to many other natural pigments.

The plant is monotypic meaning it is the only member of the genus Sherardia.