Chromosome numbers of 442 clones of Saccharum spontaneum from various parts of the eastern hemisphere are presented. About 31 numbers ranging from 40 to 128 are so far known to occur in Saccharum spontaneum, of which about nine occur with markedly higher frequencies than the rest. Groups with chromosome numbers which are multiples of eight seem to have a higher survival value than those with others.
The distribution area is divisible into three Sectors: the Western with a chromosome number range of 112-128, the Eastern with a range of 80-112, and Central with 40-80. The Central Sector appears to have had a higher evolutionary activity in the species than the other two sectors.
The lowest numbers 40 and 48 occur in India, in the Gangetic valley sub-montane to the Central Himalayas, and also in the four south-eastern deltaic areas, Since the area encompassing the locations of low chromosome number groups has also the largest concentration of chromosome numbers, it is of cytogeographic interest.
The 54-chromosome group is believed to extend along various river basins from the Aral Sea to the Bay of Bengal. The 64-group is somewhat ubiquitous in India, dominant in the peninsula; Central India has mostly 62 to 72-chromosome clones to the exclusion of other numbers. The 80-chromosome forms occur restrictedly in Nepal, Assam and the Western Ghats.
The number 112 occurs both in the Western and Eastern Sectors, but the two groups are probably distinct. 80 and 96 are conspicuously absent from the area between India and Africa. The forms of the Western Sector have many distinctive characters in common. They are probably of autopolyploid origin.
In the Eastern Sector, the typical numbers are 80, 96 and 112. In most of the areas, 80 and/or 96 occur to the exclusion of other major numbers, whereas Java, Sumatra and Borneo have almost exclusively 112-chromosome forms. The 80-chromosome forms form a continuous chain from Nepal to Fiji, by-passing the major part of Indonesia.
64-chromosomes occur exceptionally in Burma, Malay and Mauritius. These are believed to be accidental introductions from India. By analogy, the presence of the 112-chromosome forms in the China-Japan area may be attributed to Chinese trade activity with Indonesia.