Sow thistle is not a thistle as the common name implies, but it belongs nevertheless to the Thistle Family, Compositae. The genus Sonchus, according to Hegi (1931), is widely distributed in cultivated parts of the temperate and even the subtropical world, and the four ruderal species, now extending their range in North America, are found in Europe, Asia, parts of Africa, and South America. They include the perennials Sonchus arvensis L. and Sonchus arvensis L. var. glabrescens Guenth., Grab., and Wimm. as well as the annuals Sonchus asper (L.) Hill and Sonchus oleraceus L
