Abstract: The present paper discusses the classification, distribution, systematic relationship and origin of the genus Euchresta Benn. Euchresta is distributed roughly in East and Southeast Asia. The Chinese name “Shan-dou-gen”(山豆根) first appeared in “The Medicinal Herbs of Sichuan “(蜀本草) in the Song Dynasty. Afterwards there were accounts of this name in “A Materia Medica of kaibao”（开宝本草）, and “The Illustrated Classic Herbal”(图经本草) by Su Sung (苏颂). In the MingDynasty, “Shan-dou-gen” was adopted in “ Materia Medica with Commentaries” (本草纲目) by Li Shih-chen (李时珍)^［1］and it has recorded for quite a long time until now. However, because the root of Euchresta japonica Hook. f. ex Regel. is a Chinese medicine used for detoxification, and relieving pain and pharyngitis, many medicinal plants, whose roots have the same effect, are also called “Shan-dou-gen” . They are Arcisia (Myrsinaceae), Cyclea, Pericampylus, Stephania, Menispermum (Menispermaceae), Helicteres (Sterculiaceae) , Beesia (Ranunculaceae) , Sarcococca (Buxaceae) , Sophora, Atylosia (Leguminosae), etc. However, the name should be used only for Euchresta japonica according to the Chinese botanical literature. The genus was established by J. J. Bennett in 1838, based on Andira horsfieldii Lesch. (1810) ( =E. horsfieldii (Lesch.) Benn.) from Java, It was classified in the subtribe Geoffroeeae of the tribe Dalbergieae by Bentham (1860) and Bentham et Hooker (1865). There were two species then, i. e. E. horsfieldii and E. japonica. In 1970-1978, H. Ohashi and his co-workers published a series of outstanding works on Euchresta, in which H. Ohashi established a new tribe-Euchresteae Ohashi, that contains only one genus-Euchresta, and suggested a clearly close relationship between the genus under study and the tribe Sophoreae, especially Sophora, and also considered that the ancient group of Euchresta was in between New Guinea and Australia and extended northwestwards to islands and the continent of Asia. He described 4 species and reduced two species, i. e. E. trifoliolata Merr. (1922) from Guangdong, China (=E. japonica) and E. strigillosa C. Y. Wu. Wen (1984) published E. longiracemosa S. Lee et H. Q. Wen ex H. Q. Wen from Guangxi, China, as new. Five species are included so far in this genus. This paper reports 4 species and 3 varieties: i. e. E. japonica, E. horsfieldii, E. horsfieldii var. laotica, E. formosana, E. tubulosa, E. tubulosa var. longiracemosa, and E. tubulosa var. brevituba, which are grouped into two sections (Fig. 3). i. e. Sect. Euchrestae and Sect. Tubulosae. Sect. I. Euchrestae without a long tube at the base of calyx, comprises 3 species, 1 variety and is distributed in southern Honshu of Japan, southern Yunnan of China, northern Indochina Peninsula, and Java of Indonesia. The section forms three discontinuous distribution patterns: 1) E. japonica is of Sino-Japanese discontinuous distribution; 2) E. horsfieldii is of Himalayas-Indochina-Java discontinuous distribution; 3) E. formosana is of Taiwan-Ryukyu-Philippines discontinuous distribution (Fig. 2). From what has been stated above, this section may be the primitive group, of which E. horsfieldii and E. formosana have evolved from E. japonica. Sect. II, Tubulosae, with a long tube at the base of calyx, comprises 1 species, 2 varieties and forms an island disjunction with its centre in Hubei, Hunan and Sichuan of China. The two sections are considered to have stemed from the same extinct primitive group and developed along different directions, with the distribution centre in Central and South China (Fig. 3) There are many opinions on the systematic position of Euchresta. Bentham and Hooker (1865) placed it in the tribe Dalbergieae. Baker ( 1878), Nakai (1940) and Hutchinson (1964) holded Bentham and Hooker’s opinion, while Nakai (1940) established a subtribe, Euchrestinae Nakai, and considered Euchresta related to Mullera Linn. F. and Andira A. L. Juss. According to the morphological, cytological and biochemical data, Ohashi (1970-1978) clearly suggested a close relationship between the tribe Euchresteae and the tribe Sophoreae, which are different from the genera in the tribe Geoffroeeae as well as the tribe Dalbergieae (s. l.). He also recognized the similarity between Euchresta and Sophora, especially S. bhutanica and its allied species. Polhill and Raven (1981) holded Ohashi’s opinion, but the relationship of the tribe Euchresteae was put between the tribe Crotararieae and the tribe Thermopsideae hermopsideae, far from the tribe Sophoreae. We agree with Ohashi, but we think that Euchresta is most closely related to the genus Maackia, especially judged from the chromosomal number and the chemical composition, which is in accordance with M. Tenuifolia (Hemsl.) Hand. -Mazz. ( Mizuno et al. 1990). Therefere, the relationship of Euchresta with its allied genera is suggested as in Fig. 4. Based on the habitat and distributional area of Euchresta, it is inferred that its ancestor was a member of the Tertiary-paleotropical mountain forest flora and then distributed in the whole forest region. It is considered that the genus originated in Cathaysia. The distributional area of Euchresta lies in the area west of “Wallace’s Line”, a famous biogeographic line. Many botanists and zoologists have discussed this line, but they have also proposed many modified biogeographic lines for this area (Brown and Gibson 1983) e. g. “Huxley’s line” (including modifications); “Sclater’s line”(1858); “Weber’s line” (1902); “Lydekker’s line”; Merrill’s line” (1923) etc., (Fig. 2), of which “Wallace’s Lin” and “Lydekker’s line” are accepted by many zoogeographers. However, Schuster (1972) expounded “Wallace’s line”based on more pieces of evidence from geology, zoography, and distribution of land plants (including Hepaticae, Conifers, and Angiospermae). Thus Schuster stated: (1) The narrow channel between the Australian bloc and Eurasian one was still an effective barrier for many groups of organisms as recently as 10-15 m. y. ago. (2)The amount of movement-or transgression-across this barrier varies from group to group. Organisms -presumably “modern” and “successful”-with strong powers of movement have transgressed to a larger extent than taxa belonging to old, “senescent”and (usually) stenotypic groups. Thus it can be said that Euchresta is an age-older group and distributed only in the area west of “Wallace’s Line”. It is also known from the information of paleogeography and paleobiogeography: up to about 50 m. y. ago Australia and New Guinea moved progressively northward from warm temparate into the tropics, crossing the Tropic of Capricorn at about the beginning of the Miocene (25 m. y.), and coming into more or less direct contact with the proto-Indonesian at the middle Miocene (-15m. y.) (Axelrod & Raven, 1982). At that time, Euchresta was only distributed in Asia (including Philippines and Java) and formed the present dispersal-patterns, but it has never reached New Guinea and Australia (i. e. southeast of“Wallace’s Line”, because New Guinea and Australia plates were still on the way northward. Therefore, we think that the original place of Euchresta could not lines between New Guinea and Australia, and thus the actual significance of “Wallace’s Line” is not only a demarcation line between Laurasia and Gondwanaland but also a demarcation line between the Laurasia Flora and the Gondwana Flora for Asia and Australia.

Key words: Euchresta, Classification, Distribution, Systematic relationship, Phytogeography “Wallace’s Line”