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Perennial herbaceous plants are a key element of the vegetation cover in arid lands, during a long period of the year, but their persistence depends on their ability to cope with acute drought. This characteristic could become very important with the predicted climatic changes in arid lands because the persistence of perennial plants will be a key element countering the process of desertification. The aim of the present study was to compare experimentally the response to water deficit of different genotypes of the perennial grass Cenchrus ciliaris L. (buffelgrass). We analysed the impact of water deficit on productivity, time span of the vegetative growth and leaf traits. Overall, there was highly heritable variation in the responses to applied water deficit for the measured attributes, and five different groups of genotypes responded differently to water deficit. These groups of genotypes differently invested their energy to alter their phenotype in response to water deficit. Consequently, some genotypes were more strongly affected by the water deficit and their aboveground biomass showed the largest decrease. The group of genotypes which showed the smallest decrease of their aboveground biomass was characterised by less increase of leaf hairiness, a strong decrease of leaf area and also the strongest decrease of stomatal density on the abaxial epidermis. The current study provides evidence that the capacity of C. ciliaris to regulate its growth as an adaptive mechanism under water deficit is dependent on strong genetic variation that could affect its productivity and in consequence the vegetation cover of arid ecosystems.