SOW THISTLE, the popular name given to a species of a genus of composite plants, Sonchus. There are about 50 species, mostly herbaceous, but some forming shrubs or small trees. Some of the first may be considered cosmopolitan, while the woody sorts are almost restricted to the Canaries and to the island of Madeira. The most common species in Great Britain is the common sow thistle, Sonchus oleraceus. It is very abundant as a weed, is greedily fed upon by many animals, and is sometimes used on the European continent as a pot-herb. It grows to a height of two or three feet, with a branching stem and small yellow flowers. The S. alpinus forms a tall and fine plant, with fresh and sharply defined foliage and large heads of beautiful blue flowers. The S. arvensis is found in Massachusetts and southern New York.