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Weathering features are described from a meteorologically arid area in southern Tunisia. Active weathering is concentrated in topographic lows (pits and pans) that concentrate available moisture and are associated with endolithic and epilithic algae responsible for algal boring, plucking and etching of the limestone substrate. Deposits of gypsum have concentrated through evaporation within hollows and occur as isolated patches of tabular crystals indicating an additional weathering agent characteristic of arid environments. The active development of a complex microkarst and associated salt weathering are combining to destroy linear karstic features such as rillenkarren, widespread case-hardening and in places patches of iron- and manganese-rich rock varnishes. The complexity of active and inherited weathering features belies the perceived simplicity and lack of weathering opportunities associated with aridity. Instead it focuses on the need to consider the nature of microclimatic conditions at the rock/air interface especially when seeking to define desert weathering environments. It also highlights the difficulties of interpreting polygenetic landforms and the importance of microscale studies for identifying the impact of contemporary climatic conditions. Copyright (C) 2000 John Wiley & Sons, Ltd.