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The composition of cyanobacteria, mosses, and lichens of biological Soil Crusts were correlated with soil characteristics and sun exposure along an environmental transect. The study was conducted in Zapotitlan drylands, a locality within the Tehuacan-Cuicatlan Valley, central Mexico, where a great variety of environments for crust development exist due to landscape fragmentation. Data were analyzed with redundancy and Sorensen analysis. Soil crusts consisted of different combinations of cyanobacteria (7 species), mosses (19 species), and lichens (8 species). The relative frequencies of these groups were positively correlated with soil apparent density and lichens were also positively correlated with soil pH. However, there were no significant correlations with sun exposure. (C) 2009 Elsevier Ltd. All rights reserved.