The global distribution of tribes of the gramineae in relation to historical and environmental factors

Abstract

An extensive survey of the literature on grass distribution throughout the world has been made to determine the average percentage of species of each of the major grass tribes in the total grass flora. These average percentages for the six largest tribes are as follows: Agrosteae 8.2 per cent. Eragrosteae 8.1 per cent. Andropogoneae 11.9 per cent. Festuceae 16.5 per cent. Aveneae 6.3 per cent. Paniceae 24.7 per cent. The distribution of each of the above tribes is shown on world maps, and the relationship of this distribution to climatic, historical, and taxonomic factors is discussed. It is shown that the present distribution of each of the major tribes can be explained by a few readily recognizable factors. Climatic factors are of primary importance in relation to grass distribution and winter temperature has special significance.