Two natural populations of Malachra capitata (Malvaceae) designated as Group-I and II were studied under daily circadian rhythm as well as artificial night illumination for ascertaining the occurrence of night sleep or nyctinasty in the species and its possible ecological advantage. The Group II population, exposed to 24 hours of illumination evinced higher values for vegetative growth as measured by their leaf size, number of leaves and plant height. However, these same plants expressed reduced or no sleep movement in absence of alternating light and dark phases. On the contrary, the Group I population experiencing natural circadian cycle of 12 hours simultaneous light and dark phase had lower values for the same vegetative growth variables. The plant biomass and flower production values in Group–I plants was higher than that of Group-II. A scatter-plot for flower production and total plant biomass in Group–I had a strong correlation with R value of 0.75. The same correlation for Group–II plants had R-value of 0.27 only. Hence, Group-I plants that experienced night sleep showed a strong and positive correlation between biomass accumulation and flower production. Though the vegetative growth variables were lower for Group I, their higher biomass was contributed mostly by the large number of flowers and the elaborate arrangement of the flowers in the inflorescence. In M. capitata the inflorescence has 3-7 heads at each leaf axil. Each head in turn has 2-5 flowers encircled by 3 or 4 conspicuous leafy bracts and bracteoles. The flowers also have a long pedicel and fruits having 5 seeds in the schizocarp. Thus, the reproductive units of the species accumulate a substantial part of the biomass. This is the first report of nyctinasty in M. capitata and its assistance in flower production. Hence, it is possible that nyctinasty provides an ecological advantage to the plant species by diverting resources from vegetative activities towards reproductive activities. Therefore, the role of nyctinasty in facilitating biomass accumulation and partitioning of plant resources for reproductive success in plants requires further investigation