More than 400 species of plants in eight genera are found in tropical and subtropical regions except for Australia, especially in South America, and a few in temperate zones; in China, there are four genera and more than 70 species of Aristolochia, Asarum L., Bragantieae and Sarumeae. Except for a few areas, they are produced throughout the country, with Sarumeae being a single genus endemic to China. Most of the species in this family, such as Asarum sieboldii, Asarum insigne Diels.,Asarum forbesii Maxim., Aristolochia, Radix Aristolochiae Fangchi and Sarumeae, are commonly used in traditional Chinese medicine, and many are also beautiful ornamental plants. The flowers are nearly 40cm in diameter and are borne singly on old stems; their unique morphological structure has resulted in a unique pollination method: their tepals are only 1 piece, inflated at the base like a cucullus with a constricted neck, enlarged at the top like a flag and covered with purple-brown spots or stripes; the inner side of the perianth tube of the delicate flowers has hairs growing inwards, the bottommost part is the pistil and the stigma is close to the anthers. The spots on the perianth and the odour emitted attract small insects to the back of the “pocket” for pollination, where they enter the “pocket'” but are prevented from doing so by the hairs on the inside of the perianth, sometimes staying for several days to feed on the plump cells on the perianth. The hairs do not shrivel until the pollen has matured and been dispersed on the insect’s back. The fly carrying pollen flies to another flower, where it encounters a mature stigma and is ready for pollination. The stigma matures before the stamens and if it has already received pollen from a different flower, the flag-like material on the outside of the perianth loses its expansion and covers the perianth tube, leaving the whole flower pendulous and inaccessible to flies.