Abstract
Thirtyfive taxa under five genera of the family Commelinaceae have been studied cytologically. Different populations of the same species collected from different regions of Eastern India have also been studied. The chromosome numbers determined range from 2n=20 to 120.
The chromosome complements of different populations of the same species have been found to differ from each other not only in the number but also in the structure of the chromosomes to a greater or lesser extent. In the origin of different members of the family studied here, structural alterations have been as important as the changes in the number of chromosomes, in the evolution of new forms. In speciation in this family as seen from chromosome number records allo and aneuploidy have played much more important roles than autopolyploidy.
Variations in the chromosome complements in somatic nuclei of the same individual have been found in some cases. Since all the species are propagated profusely through vegetative means, the occurrence of varying numbers in the somatic tissue obviously provides scope for the origin of new types; through their entrance into the growing apex of daughter shoots.
In view if the data obtained so far, it has been suggested that there are two major chromosomal lines within the family Commelinaceae, one starting from a basic set of 4 or 5 comparatively short chromosomes, the other from a basic set of 6 long chromosomes. The other numbers are apparently derived ones.
Reviewing the different systems of classification, the one followed by Pichon (1946) or Brenan (1966) has been found to be more compatible with the cytological data since they group the taxa together as climaxes of different sub-lines of evolution. Cytological evidences are more in favour of them rather than of the systems recognising only two major groups within this family.
