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Studies in arid environments have evaluated the effect of groundwater variation and simulated precipitation on plant production and vegetation condition but it is unclear if plants respond equally to the availability of surface water or groundwater.  This study was conducted in a greenhouse to evaluate growth and physiology of three desert graminoids (Distichlis spicata, Leymus triticoides, and Juncus arcticus) as affected by surface water availability (mimicking precipitation) or subsurface water availability (mimicking groundwater).  The species of study are amply distributed in wetlands and open rangelands of western USA and were collected from two sources of ecological distribution: an area near Bishop, California, and an area near Burns, Oregon. We had two general hypotheses: 1) that the use of surface water is favored over groundwater and 2) that there are ecotypic differences in the response of the species to water availability. We examined the hypotheses by growing the species in two-layer pots in which soil water content in the upper and lower layers was controlled independently. Plants were subjected to one of three watering treatments: water applied only to the upper layer, water applied only to the lower layer, or water applied both to upper and lower layers.  The first hypothesis was partially supported by the results of the study, but variability existed among species. However, when all species had equal access to both surface soil water and groundwater plants tended to preferentially use surface water.  The second hypothesis was clearly supported by our results.  Although the mechanism is not clear, it is possible that an area with periodic and predictable shallow groundwater underlying a dry or saline soil layer, such as the California site, might favor plant ecotypes with high proficiency in water acquisition by deeper roots.