Origin and Distribution of Saccharum

The present paper reports an attempt to work out the origin of the genus Saccharum from phytogeographical data, corroborated by morphological, cytological, and breeding evidences. 2. The distribution of Saccharum and its congeners shows that Erianthus has the highest number of species, twenty-eight, and is most widely distributed in Asia, Europe, and America. The majority of the species of Erianthus occur in India, particularly on the slopes and foothills of the Himalayas in eastern India and in America. Saccharum has in all five species occurring in India, Malaysia, and China, of which four occur in India. Sclerostachya has three species, two of which are found in India, and Narenga has two species, distributed in India, Indochina, and China. Hence the maximum concentration of species belonging to these four genera is in India. 3. It is suggested that the Saccharum complex originated in the Indo-Burma-Chinese region and spread to adjoining areas. It is quite likely that Saccharum, Sclerostachya, and Narenga had a common origin in Erianthus. It is significant that some species of Erianthus have the lowest chromosome number (2n = 20) in the Saccharum complex and that E. procerus (Roxb.) Raizada, E. arundinaceus (Retz.) Jesw., and E. elephantinus Hook. f., occurring in northeastern India, look very much like sugar cane in their robust culms. Further speciation in Saccharum might have taken place by polyploidy and hybridization. Useful mutants, such as forms with a high sugar content, have been perpetuated through clonal propagation by human selection, namely, S. barberi in India and S. sinensis in China; S. robustum has, on the other hand, evolved by natural selection in New Guinea. S. officinarum is also indicated to have originated in India, because the origin of S. barberi in India by hybridization of S. officinarum with S. spontaneum presupposes the presence of the former species in India from very early days. Further evidences in support of this view are presented in the paper.