Plants growing in serpentine soils have to cope with low concentrations of major nutrients and often with toxicity caused by heavy metals. In addition, serpentine soils generally have low water holding capacity and thus plants growing on them are usually adapted to water stress. In California, two different ecotypes of Bromus hordeaceus are found in sandstone and serpentine soils. In order to compare their tolerance to water stress, both ecotypes were grown for 3 months in serpentine and sandstone soils and submitted to water stress regimes. In our experiment soil texture proved to be a major constraint for plant growth in sandstone soils especially under water stress. Growth responses and root branching patterns of the serpentine ecotype of B. hordeaceus showed greater physiological adaptation to stress conditions caused by water deficiency and soil texture.