Chromosomal Conspectus and Evolutionary Status of Indian Commercial Timbers (Hardwoods)

Abstract

Numerical variability in hardwood timbers is observed from the great variation in chromosome numbers (2n=10 to 2n=196) as well as basic numbers (x=5-21, 23, 31 and 43). The most commonly represented chromosome number is 2n=24. Treating x=7 as the original base number for angiosperms, the possible role of polyploidy and/or aneuploidy in the origin of existing heterogeneity in the present day base numbers of Indian commercial timbers is discussed. Incidence of polyloidy is 33.3%. Amongst polyploids the tetraploids are the most common. Intraspecific polyploidy exists in 36 species. The highest level of ploidy 28x is in Bischofia javanica. The average somatic chromosome number in the present sample of timbers is quite high (38.15), this duly compensates the low recombination index resulting due to small sized chromosomes, a characteristic of majority of the hardwood timbers. Other phenomena of cytological interest are the existence of B-chromosomes (9 species) and cytomixis (8 species). There appears to be no consistent relationship between chromosome number and economic usefulness of tropical hardwood timbers.