In the present Study, Physcia semipinnata samples were exposed to UV-A (352 nm) in 20 J m (2) for 24 h, 48 h and 72 h to seek the alterations in the PSII photosynthetic quantum yield, thallus anatomy and DNA mutation rate in response to radiation. The Fv/Fm ratio decreased in 1 semipinnata following expoSure to UV-A for 24 h, 48 h and 72 h. The data of the present study reported that Chia degradation Occurred by exposition of UV-A for 24 h. 48 h and 72 h. Photobiont size and thickness of upper cortex layer also showed a gradually decrease in P. semipinnata thallus sections during 24 h. 48 h and 72 h. The thickness of the upper cortex layer, exposed to UV-A for 72 h, of R semipinnata thallus reduced 64%, compared with control. The random amplified polymorphic DNA (RAPD) technique was used to detect DNA damage. The main changes observed in the RAPD profiles resulted in both appearance and disappearance of different bands and variation of their intensity. According to RAPD assay, the genetic distance between the control group and 24 h. 48 h and 72 h UV-A exposed, groups Was found 56%, 78% and 84%, respectively. (C) 2008 Elsevier B.V. All rights reserved.