Abstract: This revision deals with the system, evolution, distribution, cytotaxonomy and taxonomic treatment of the genus Aristolochia Linn. from E. & S. Asia, which covers Japan, USSR (Far East), China, Viet Nam, Laos, Cambodia, Thailand, Burma, India, Bhutan, Nepal, Sikkim, Bangladesh and Pakistan. Total 2 subgenera, 7 sections, 4 series, 68 species and 1 variety (cultivated species not included) are recognized in this treatment, of which 3 sections and 2 species are described as new. In addition, 13 new synonyms and some new records to this region are also included. Ystem Having estimated all the works dealing with the subdivision of the genus by the previous authors, the system of O. C. Schmidt (1935) is chosen as the basis, with a change of the sequence of the subdivisions. The subgenus Pararistolochia (Hutch. & Dalz.) O. C. Schmidt, which has indefinite stamens and gynandrous lobes, seems to be better considered as the most primitive one in the genus, while the subgenus Siphisia (Raf.) Duch., which has definite stamens and gynandrous lobes, anthers arranged in 3 pairs and more modifications of the perianth, seems to be the most advanced one. The perianth of the subgenus Siphisia has differentiated into several types, and it is more rational using this character to classify sections than lobes of the gynostemium. In this way, three new sections has been established. A suggested system of the genus is summarized as follows: Subgen. 1. Pararistolochia (Hutch. & Dalz.) O. C. Schmidt Subgen. 2. Aristolochia: Sect. 1. Aristolochia (2 series), Sect. 2. Gymnolobus Duch. Subgen. 3. Siphisia (Raf.) Duch.: Sect. 3. Pentodon Klotz, Sect. 4. Odontosiphisia J. S. Ma, Sect. 5. Leptosiphisia J. S. Ma, Sect. 6. Nepenthesia Klotz., Sect. 7. Obliquosiphisia J. S. Ma, Sect. 8. Siphisia (2 series). Evolution According to the character analysis of the genera of Aristolochiaceae, the evolutionary trends of the family are proposed as follows: 1, the perianth from double to single, from cup-like to tubular, 2, stamens from indefinite to definite, from separate from pistil to united into a gynostemium with pistil, which is a major evolutionary line in the family, 3, ovary from half-superior to inferior, and 4, fruit from a follicle to a capsule. It is evident that the genus Aristolochia, with a tubular perianth, stamens 6, a gynostemium, an inferior ovary and a capsule, is in highly advanced position in the family. The subgenus Pararistolochia, which has more stamens and more lobes of gynostemium, is very similar to the genus Thottea Rottb. and thus better considered as the most primitive subgenus in the genus. The subgenus Siphisia, which has definite stamens (6) in 3 pairs and 6 lobes of gynostemium as well as the polyploid feature (2n=4x=28), is the most advanced subgenus. As a result of the character analysis, the evolutionary trends of the subgenera in the genus, which are in accordance with those of the family, are proposed as follows: 1. stamens from indefinite to definite, and 2. gynostemium lobes from more to less. Distribution The more primitive subgenus Pararistolochia is only distributed in West Africa (except 1 species in Malesia), the subgenus Aristolochia in the tropical and subtropical regions, rarely in the temperate one, and the most advanced subgenus Siphisia occurs mainly in E. Asia, occasionally in N. America. The result of this work shows that the Hengduan Mountains is the second center of distribution after South America. The second center of distribution is of following features: 1. complex composition of taxa, among 3 subgenera and 8 sections, 2 subgenera and 7 sections have been recorded here, 2. rich in species, more than half of the total E. & S. Asian species, i.e. about 42 species have been found in this region, and 3. numerous endemics, more than 85 percent of the total number of species in the region, i.e. about 35 species, are endemic. Cytotaxonomy and taxonomic treatment The known chromosome numbers in 43 species, with 34 reported by Gregory (1956) and Fedorov (1969), together with 9 species newly reported in this work, show that Subgen. Aristolochia with 2n=2x=14, rarely 12, is apparently more primitive than Subgen. Siphisia with 2n=2x=28.

Key words: Aristolochia, Revision, System, Evolution, Distribution, E.Asia and S.Asia.