Morphology, anatomy, secondary chemistry, ecology, and distribution of Rhizocarpon geographicum (Rhizocarpaceae, lichenized Ascomycota) in north-eastern Iran are investigated and discussed. 1. Introduction Iran has an exceptional variety of biomes which has resulted in an extensive diversity in many organism groups including lichens. The history of lichenological exploration in north-eastern Iran is fairly extensive, dating back to the middle of the twentieth century [1, 2]. Since 2004, however, the investigations in the present Khorasan provinces have much increased due to the development of local expertise. The total number of the species reported from the region represents the crustose growth form as the dominant lichens [3–7]. Among the genera is the well-known and conspicuous yellow-green group of Rhizocarpon which is abundant in Arctic-Alpine environments worldwide. It grows very slowly (0.02–2？mm？yr？1) and lives to a considerable age [8]. The present paper is part of a series of studies intended as contributions towards a detailed treatment of Iran’s lichen biota. 2. Materials and Methods Field investigations were made by a party of two people during May–November 2006 and July 2007 with some more collecting in 2011. A total of 15 sampling sites were visited, situated in Razavi Khorasan province (127432？sq.km), which lies between 33°52′–38°17′N latitudes and 55°17′–61°15′E longitudes in north-eastern Iran (Figure 1). The study area belongs to the Irano-Turanian phytogeographical region [9]. Calcareous bed rock is predominant in the study area [10] and the elevation of the sites ranges from 1340 to 1880？m. Over 537 Rhizocarpon thalli were investigated of which 311 (58%) belong to R. geographicum. As a result much new information became available on the species of Rhizocarpon [11–13]. Morphological and anatomical characteristics of the thalli and fruiting bodies were examined with a stereomicroscope and a light microscope. Preparations were made in distilled water, 10% KOH and KI. The usual color tests were done by applying the reagents on the thallus or on exposed medulla [14]. The areoles of the thallus were separated under stereomicroscope and were extracted in acetone. Then the extractions were studied using two standard solvents, GAW and GE, on the basis of recrystallization of the soluble compounds [15]. Three specimens were subjected to thin-layer chromatography by M. Kukwa (Gdansk, Poland), S. R. Clayden (New Brunswick Museum, Canada), and the author by using solvent C. The description below is based on these observations. Vouchers are
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