the expansion in the use of glyphosate as herbicide in order to control weeds, mainly in transgenic soybean cultivation, causes biological and ecological deterioration in the ecosystem. the species u. amblyoclada has been used as biomonitor "in situ", in order to estimate this herbicide′s effect in the lichenic flora. thus, the samples were transplanted during a 3-month period in a soybean field and in a control area. after that, physiological parameters indicating lichenic damage were established. furthermore, the effect of different herbicide doses on the lichen’s physiology was tested in the laboratory. the results showed a meaningful decrease in the photosynthetic pigments after the fumigation with glyphosate. a significant decrease of the contents was observed of feofitina ‘a’ and ‘b’ and, in addition, an increase in the concentrations of the products of oxidations of cellular membranes. these results were observed also in the experiments in laboratory. in this way, the damaging effects of glyphosate on the lichen u. amblyoclada and the usefulness of this species as biomonitor in agricultural areas were demonstrated.