Phytotoxicity is a toxic effect by a compound on plant growth. Such damage may be caused by a wide variety of compounds, including trace metals, pesticides, salinity, phytotoxins or allelopathy. Fossil fuels are still the main source of energy representing approximately 80% of the total world supply. However, its exploration, recovery and use present serious environmental problems, which are mainly associated with the production of greenhouse gases and contamination of land and water resources. Phytoremediation is an alternative to more expensive remediation technologies because it is a feasible, effective and non-intrusive technology that utilizes natural plant processes to enhance degradation and removal of contaminants from the environment. Phytotoxicity studies with crude oil on native Brazilian trees included plant growth, root length, produced biomass, tissue analysis, etc. Typical phytotoxicity studies with trees for phytoremediation application also include elaborated research on uptake potential, metabolic pathways, in vitro systems with cell suspension, hairy root cultures, etc. The effect of diesel oil on plant transpiration during the “free phase†experiment is represented by the normalized relative transpiration. S. parahyba showed decreased transpiration in the presence of diesel in all doses tested. Transpiration was reduced by 53%, 42%, 59% and 26% at 8, 16, 33 and 66 gL-1, respectively.