Biosystematic Studies on Indian Commelinaceae - The Chromosome Pattern and Evolutionary Trends

At present the family Commelinaceae in India comprises 80 species under 10 genera excluding, however, all ornamental, and cultivated species which are mostly exotic. While revising the family an attempt has been made to blend classical taxonomy with experimental taxonomy and to analyse as to how far the other allied fields help for a better understanding and interpretation of the many ambiguities and "species complex" that could not be solved by the earlier herbarium methods of study. This coordinated approach has certainly indicated the splitting up of Cyanotis (sensu lato) into three distinct genera, separation of Murdannia from Aneilema, retention of Aclisia under Pollia and possibly justifies the resurrection of Dictyospermum and creation of a new genus Tricarpelema. Further, the studies have thrown light on the evolutionary trends in progress in Commelina, Cyanotis, Murdannia and Aneilema, the role of aneuploidy in speciation and as to how the polyploids through genetic isolation have played a major role in the evolution of new taxa thus enabling to invade new territories. The cosmopolitan Commelina erecta that is widespread from N. Australia to Africa through Malaysia, India and Ceylon exhibits a wide range of polyploidy (n = 30, 45 to 60) which perhaps accounts for its extreme diversity. The close similarity of the diploids and polyploids possibly suggests autopolyploidy but at least in some species of Murdannnia, as in M. vaginata, M. loriformis and M. simplex, the presence of dissimilar bivalents suggests allopolyploidy. In Cyanotis (sensu stricto) genetic and geographical isolation have permitted accumulation of differences leading to taxonomic diversification and new species have evolved mostly through aneuploidy. The genus Belosynapsis which is an off-shoot from a Cyanolis ancestor has a different habitat altogether and all the three species of the genus (two Indian and one Malesian) are distinctly epiphytic or lithophytic. In some cases the new gene combinations have been successfully retained by vegetative propagation either by proliferating at the nodes (as in Cyanotis adscendens) or through development of underground bulles (as in Cyanotis arachnoidea var. thwaitesii and Murdannia juncoides) and as a result, the annuals have turned into perennials. A tentative phylogenetic chart is presented indicating possible lines of evolution within the family.