Plant species diversity
© Barthlott, W., Biedinger, N., Braun, G., Feig, F., Kier, G., and Mutke, J. (1999): Terminology and methodilogical aspects of the mapping and analysis of global diversity. Acta Botanica Fennica 162, 103-110.
Many hypotheses have been proposed to explain why species richness is greater in tropical latitudes than near the poles.