The Prickly sow thistle (Sonchus asper) belongs to Asteraceae (the Aster family). It is a biennial herb that is native to Europe. This herb was introduced into Japan in Meiji Era (about 120 years ago). It grows in roadsides or waste places and can reach 50-100 cm in height. It passes the winter by radical leaves and extends midair stem in spring. The leaves enfold stems, and have prickly-pointed toothed edges. The yellow ray flowers come in March to October.