In the desert areas of Israel there is hardly any place where rock surface is devoid of one or another kind of poikilohydric lithobiont. When dry, their thallus is dormant, but when wetted they rapidly resume physiological activity. Microscopic organisms such as cyanobacteria, lichens, and non-lichenized fungi, have constant specific impact on weathering of rocks. Typical kinds of rock surfaces are thus formed in association with each lithobiont community. In each climatic zones of Israel specific morphological types of weathered surfaces are confined to certain geomorphologic positions. Hard limestone rocks, with water holding capacity of 0.5-2.0%, at the Negev Highlands, subjected to 100-150 mm mean annual rainfall, are reported here. Epilithic crustose lichens cover most of the rocks at north-facing slopes. They protect the surface from direct deterioration by splashing raindrops. Efficient solar radiation over the south-facing slopes induces harsh microclimatic conditions. In the newly exposed surfaces the drought resistant fungi Lichenothelia species cause minute pits by dissolving the rock around their 0.1- 0.2 mm globular body. Establishing in the micropits, cyanobacteria and cyanophilous lichens, which cause faster weathering in their close vicinity, lead to the formation of hemispheric depressions, 2-10 mm diameter, in the rock. More porous limestone, with 10-15% water holding capacity, looks like the previous, but supports cryptoendolithic filamentous cyanobacteria. Chasmoendolithic coccoid cyanobacteria cause or accelerate deterioration in mainly south-facing slopes. The specific morphology in these places is known as exfoliation. Detached stones in that area enjoy moisture of dew in addition to the rainfall water. They support euendolithic lichens, which cause jigsaw puzzle-like pattern on the stone surface. When rolled on slopes these stones display all their faces to the atmosphere and thus become weathered in a jigsaw pattern throughout. Pitting organisms on are common on man-made marble monuments in more mesic areas of Europe.

Key words: cryptoendolithic filamentous cyanobacteria, cyanobacteria, jugsaw puzzle-like pattern, Lichens, pitting