Diffuse vegetation is made up of dwarf shrubs and/or perennial grasses sparsely but regularly distributed in the landscape. It characterizes Mediterranean and temperate climate steppes. Contracted, i.e., clustered, vegetation, on the other hand, refers to vegetation irregularly distributed over the landscape, concentrating in the lower parts of the topography where some runoff mitigates the overall edaphic aridity, the interfluves remaining devoid of perennials. The distribution of diffuse and contracted vegetations depends on the substrate and on the intensity of land use. But, by and large, it appears around the 100-mm isohyet of mean annual precipitation and below. Whenever there are some exceptions, these are analyzed. This concrete landscape limit occurs in all the true deserts of the world. It could therefore be considered as an objective limit between arid and hyperarid zones. Keywords: vegetation, desert, steppe, arid, rnhyperarid, landscape, plant ecology.