We studied morphological and growth responses to drought of two sub-populations of Bromus pictus from communities with soils with different water availability from the Patagonian steppe. After a process of acclimatization common to both sub-populations, individuals from both sub-populations were subjected to three levels of water availability during 44 days. Independently of the water availability treatment, the sub-population from the community of high soil water availability showed higher aboveground relative growth rate (RGR) and higher leaf size (area and weight) compared to the sub-population from the community of low soil water availability. These results prove the expected evolution of higher growth rates and leaf sizes in resource rich environments. The sub-population from the community with low water availability also showed a higher tillering rate and a more prostrate morph than the sub-population from the community with high water availability. A higher number of small tillers may be a useful strategy for a quick response to water inputs and for distribute the risk of drought-induced mortality. A more prostrate morph may also present advantages like reducing the area exposed to dry air. The results obtained showed that soil heterogeneity may promote genetic variation. We were unable to detect statistically significant interactions between population and water availability treatments. The genetic variation found between the populations may be useful to develop breeding programs of a native species and may also increase the evolutionary potential of a native species to adapt to environmental changes