Leaves of A. annua are a plentiful source of artemisinin, a drug with proven effectiveness against malaria disease. The objective of this study was to evaluate the effect of different photoperiod and temperature conditions in the flowering of clones from one A. annua genotype whose parentages are original from Vietnanm, comparing it with a studied genotype original from China. The experiments were carried out in photoperiodic chambers located inside of plastic houses. The clones were submitted to photoperiods of 7, 9, 11, 13, 15 and 17 h, in two natural conditions of temperature: spring/summer (maxim of 37°C and minimum of 19°C) and autumn/winter (maxim of 29°C and minimum of 13°C). In advance, it can be affirmed that the Vietnanm genotype clones presented a photoperiodic behavior of Short-Day Plants (qualitative or absolute) with low temperature or vernalization requirement to have their flowering accelerated. The critical or inductive photoperiod ranged between 11 and 13 h to Vietnanm genotype and 13 and 15 h to Chinese genotype. The Vietnanm genotype plants flourished about 4-5 wk after submitted to the inductive photoperiod, while the Chinese genotype plants flourished in 2 wk. With regard to flowering, A. annua genotypes with different geographical origins can present variations in the behavior under same photoperiod and temperature conditions.569 275280Bagchi, G.D., Ram, M., Sharma, S., Kumar, S., Effect of the planting date on growth and development of Artemisia annua under subtropical climatic conditions (1997) J. Med. Aromatics Plant Sci, 19, pp. 387-394Chan, K.L., Teo, C.K.H., Jinadasa, S., Yuen, K.H., Selection of high artemisinin yielding Artemisia annua (1995) Planta Med, 61, pp. 285-287Chen, F.T., Zhang, G.H., Studies on several physiological factors in artemisinin synthesis in Artemisia annua (1987) Plant Physiol. Commun, 5, pp. 26-30Ferreira, J.F.S., (1994) Production and Detection of Artemisinin in Artemisia Annua L., , Purdue University, Purdue, EUA, Ph.D. thesisFerreira, J.F.S., Simon, J.E., Janick, J., Developmental studies of artemisia annua: Flowering and artemisinin production under greenhouse and field conditions (1995) Planta Med, 61, pp. 167-170Ferreira, J.F.S., Janick, J., Distribuition of artemisinin in Artemisia annua (1996) Progress in New Crops, pp. 579-584. , (J.Janick ed.). ASHS Press, ArlingtonGeldre, E.V., Vergauwe, A., Eekhout, E., State of the art of the production of the antimalarial compound artemisinin in plant (1997) Plant Mol. Biol., 33, pp. 199-209Klayman, D.L., Qinghaosu (artemisinin): An antimalarial drug from China (1985) Science, 228, pp. 1049-1055Laughlin, J.C., The influence of distribuition of antimalarial constituents in Artemisia annua L. on time and method of harvest (1995) Acta Hort, 390, pp. 67-73Magalhães, P.M., (1996) Seleção, Melhoramento e Nutrição da Artemisia Annua L., Para Cultivo em Região Intertropical, , Universidade Estadual de Campinas Campinas, Brazil Ph.D. thesisMagalhães, P.M., Delabays, N., Sartoratto, A., New hybrid lines of the antimalarial species Artemisia annua L. guarantee its growth in Brazil (1997) Ciência e Cultura, 49, pp. 413-415Marchese, J.A., (1999) Produção e Detecção de Artemisinina em Plantas de Artemisia Annua L. Submetidas A Estresses Abióticos, , Universidade Estadual de Campinas Campinas, Brazil, M.S. thesisMorales, M.R., Charles, D.J., Simon, J.E., Seasonal accumulation of artemisinin in Artemisia annua L (1993) Acta Hort, 344, pp. 416-420Pras, N., Visser, J.F., Batterman, S., Woerdenbag, H.J., Malingré, T.M., Laboratory selection of Artemisia annua L. for high artemisinin yelding types (1991) Phytochem. Anal, 2, pp. 80-83Woerdenbag, J.H., Pras, N., Bos, R., Visser, J.F., Hendriks, H., Malingré, T.M., Analysis of artemisinin and related sesquiterpenoids from Artemisia annua L. by combined gas chromatography/mass spectrometry (1991) Phytochem. Anal, 2, pp. 215-219Wallaart, T.E., Pras, N., Beekman, A.C., Quax, J., Seasonal Variation of artemisin and its biosynthetic precursors in plants of Artemisia annua of different geographical origin: Proof for the existence of chemotypes (2000) Planta Med, 66, pp. 57-62