Water potential (ψ w ) and water saturation deficit (WSD), and several reflectance (R) indexes were assessed in an aerophytic lichen Umbilicaria hirsuta (Sw. ex Westr.) Hoffm. The water index (WI, R 900 /R 970 ) and normalized difference vegetation index, NDVI [(R 900 -R 680 )/(R 900 +R 680 )] were strongly correlated both with the ψ w and the WSD of lichen thalli. No significant changes during desiccation were found in structural independent pigment index, SIPI [(R 800 -R 445 )/(R 800 -R 680 )]. Sensitivity of the spectral detection of water status was rather small at high hydration level (WSD < 25 %, or ψ w > -1 MPa), but this is not much limiting its value and potential use, because physiological processes in lichens are usually inhibited at much lower values of ψ w than in leaves of vascular plants.