Cleavers (Galium aparine) are herbaceous annual plants of the family Rubiaceae, which are native to North America and Eurasia. Cleavers creep along the ground and over the tops of other plants, attaching themselves with the small hooked hairs which grow out of the stems and leaves. The stems can reach up to three feet or longer, and are angular or square shaped. The leaves are simple, narrowly oblanceolate to linear, and borne in whorls of six to eight. Cleavers have tiny, star-shaped, white to greenish flowers, which emerge from early spring to summer. The flowers are clustered in groups of two or three, and are borne out of the leaf axils. The globular fruits grow clustered 1-3 seeds together; and are covered with hooked hairs (a burr) which cling to animal fur, aiding in seed dispersal.
Chemical constituents of Galium aparine include: iridoid glycosides, caffeine, asperuloside, monotropein, aucubin, phenolic acid, anthraquinone derivatives, flavonoids, coumarins, citric acid and red dye.