This book reviews the biology of bryophytes and lichens in the polar tundra, where these plants may form a dominant component of the vegetation. It considers adaptation to severe environments in terms of growth form, physiology and reproduction. The role of bryophytes and lichens is discussed in vegetation processes such as colonisation and succession, and in energy flow, nutrient cycling and other functional aspects of polar ecosystems, both natural and as modified by man, The range of microclimates experience by polar cryptograms is described using an energy budget approach, and the...