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Although arid and semiarid regions account for about 40% of world land, no nanotoxicity studies on desert plants have been reported. In this investigation, Parkinsonia florida (blue palo verde), Prosopis juliflora-velutina (velvet mesquite) and Salsola tragus (tumbleweed) were selected to determine the phytotoxicity of ZnO nanoparticles (NPs) at germination stage. Seeds were treated with ZnO NP concentrations ranging between 0 and 4000 mg L(-1). From this, the germination rate, root elongation and Zn concentration in tissues were determined. Furthermore, X-ray Absorption Spectroscopic (XAS) studies were performed to obtain preliminary information on potential NP biotransformation within plant tissues. Results indicated that germination was not significantly affected (P < 0.05) in any of the three plant species. Also, root elongation in blue palo verde was reduced by 16%, with respect to control at 4000 mg ZnO L(-1). Tumbleweed root size diminished by 14% and 16% at ZnO NP levels of 500 and 2000 mg L(-1), respectively, and velvet mesquite root length was reduced to all ZnO NP concentrations used in this study. The 50% inhibitory concentration (IC(50)) for mesquite root elongation was between 1000 mg L(-1) and 2000 mg L(-1). XAS results demonstrated that ZnO NPs were biotransformed on/within the root and Zn was present as Zn(II) in the three desert plant species.