Romerillo (Bidens pilosa var. radiata) belongs to the Asteraceae (the Aster family). It is an annual or a perennial herb that is native to tropical America. It is also naturalized in tropical and subtropical regions around the world. It is distributed in southern Kyushu, the Ryukyu Islands and the Ogasawara Islands. This herb grows in roadsides and fields, and up to a height of 50-150 cm. The stem is erect. Leaves are pentafoliolate, opposite at the bottom, alternate at the top. The flower-heads about 3 cm in diameter, with white ray flowers and yellow tubular flowers, bloom all the year round. The fruits are flat quadrilateral shaped achenes, with spines at the top.