Deserts – Overview

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A desert is considered to be one of the driest ecosystems in the world, with the expected rainfall of all deserts reaching only 0 to 20 inches per year.  Many associate the dry climate to the intense heat of a traditional ‘hot’ desert but freezing ‘cold’ deserts do exist, the biggest being the entire continent of Antarctica.  Due to the harsh climate of a desert, the vegetation found in these regions have adapted by either developing leaves and stems that store water, growing long taproots to gather water from deep beneath the surface, or developing spiny ‘leaves’ that give off less moisture than a typical leaf. 
Sources:
http://pubs.usgs.gov/gip/deserts/features/