Blue field-madder

Sherardia arvensis, the blue field-madder, is an annual herb in the bedstraw family (Rubiaceae) with trailing to ascending stems reaching up to 40 cm long. The stems are distinctly four-angled in cross-section. The rough, bristly, pointed leaves are about 1 cm long and arranged in whorls of four to six around the stem—typically six near the shoot tips and four lower down. The tiny pale lilac to pink flowers, about 3 mm across, have an elongated tube and four free petal tips; they are grouped in clusters of two or three within an involucre of six leaf-like bracts. The dry, two-lobed fruits are about 3 mm long and produce indehiscent nutlets. The species is a common weed of arable fields, pastures, grasslands, and disturbed ground across most of Europe, northern Africa, and southwest to central Asia, and has been widely naturalized in North America, Australia, and New Zealand.