Abstract: Having mixed extremely various  patterns of achenes  for a  long time in the genus Lactuca L., especially showed in the classification of it on the mainland of Asia, Lactuca  L.,  the  primary  unnatural genus,  becomes more nuclear in its limit. The present paper makes a revision to attempt providing a clear cline between Lactuca L. and its relative genera. On my opinion, only plants, represented by Lactuca sativa L., which have ovoid capitu- lum during its fruiting, numerous (7-25), yellow ligular florets and longitudinal 1-10 ribs or striae on each side of achenes, acute into filiform beak at its apex, should be defined as Lactuca L. In view of the present concept of Lactuca L., another group of plants, embodied by Lactuca indica L., having its broadening, thin winged-margin of, 1-3 striae on each side of achenes,  black, dorsi-ventral compressed, acute into thick and short beak at its apex, evident- ly, should not be placed into Lactuca L., but be regarded as genus, i.e. Pterocypsela Shih, gen. nov. Pterocypsela Shih distributes in Eastern and southern Asia, where Lactuca L. does   not occur.  In China there is all of species, seven species, of Pterocypsela Shih.  They are P.   raddeana (Maxim.) Shih, P. indica (L.) Shih, P. elata (Hemsl.) Shih P. lacciniata (Houtt.)   Shih, P. triangulata (Maxim.) Shih, P. sonchus (Lévl.)  Shih and P. formosana  (Maxim.)   Shih, But in Mediterranean regions and Middle and Western Asia mainly distributes Lactu-   ca L., in which there are only seven species from western China, Xijiang autonomic district.   They are L. dolichophylla Kitam., L. sativa L., L. altaica Fisch. et Mey., L. serriola Torner,   L. dissecta Don, L. auriculata DC. and L. undulata Ledb. With the combination of violet-purple ligular florets  non-ovoid  capitulum  during  its   fruiting, a little thick achenes, acuminate into longer. or short beak at its apex and 4-6 ribs   on each side of it, Mulgedium tataricum (L.) DC. is evidently different from Lactuca sativa L.   with combination of ovoid capitulum during its fruiting, yellow ligular florets and compres-  sed achenes, acute into filiform beak at its apex.  There seems to be no point in refusing Mu-  lgedium Cass. as a genus.  Strictly speak, Mulgedium Cass. seems to be reminiscent of Para-  prenanthes Chang (see bellow) without beak at the apex of its achenes.  In Hengduan moun-  tains and mountain range of Himalayas M. tataricum  (L.)  DC. discoveries its relative par-  tners. They are M. bracteatum (Mook. f. ex. C. B. Clarke) Shih, M. lessertianum (Wall. ex  C. B. Clarke) DC., M. monocephalum (Chang) Shih, M. umbrosum (Dunn) Shih, M. meridi-  onale Shih and M. polypodifolium (Franch.) Shih.   Having broadering and thickening margin and 4-7 striae on each side of achenes, grey,  dorsi-ventral compressed, truncate and beakless at its apex, Lactuca sibirica (L.) Benth. ex  Maxim.  (Sonchus sibiricus L.) is not only different from Lactuca sativa L. with the combi-  nation of yellow ligular florets and filiform beak at apex of its achenes, but also from the  genus Mulgedium Cass. with beak at apex of its achenes.  Therefore, Lagedium Sojak, establi-  shed by J. Sojak (1961), should be restored.  It should be point out that Lagedium Sojak is  monotypic genus excluding Mulgedium tataricum (L.) DC. with beak at the apex of its ache-  nes, non-marginated. Lagedium Sojak widely distributes  in temperate  and  frigid  zone  of  northern hemisphere.  In our country, Lagedium sibiricum (L.) Sojak, sole species of the ge- nus, restricts its northeast region. Paraprenanthes Chang, the new genus, established by Ch. Ch. Chang (1950) based on La- ctuca sororia Miq. and Lactuca yunnanensis Franch.  seems to be a distinct genus.  This ge- nus is characterized by 4-6 ribs on each side of achenes, black, fusiform, a little thick and beakless at its apex.  Besides above-mentioned two species, assigned by Chang, in forest of tro- pic and subtropic zones on the mainland of Asia there are many species with same structure in achenes like L. sororia Miq. and L. yunnanensis Franch.  The genus Paraprenanthes Chang seems to be reminiscants of Mulgedium Cass. and Lagedium Sojak, but differs from the former in its beakless achenes, from the later in its non-marginated  achenes  and 4-6 ribs on  each side of it.  In our country, there are all species of the genus known in the tropic and sub- tropic zones on the mainland of Asia.  They are P. sororia (Miq.) Shih, P. yunnanensis (Fra- nch.) Shih, P. longiloba Ling et Shih, sp. nov., P. heptontha Shih et D. J. Liou, sp. nov., P. prenanthoides (Hemsl.) Shih, P. pilipes (Migo) Shih, P. thirionii (Lévl.) Shih, P. sylvicola Shih., sp. nov., P. multiformis Shih, sp. nov., P. auriculiformis Shih, sp. nov. and P. sagitti-