The chromosome number of 30 species belonging to 16 genera of Acanthaceae from South India has been studied. Chromosome numbers determined in the present study range from 2n=16 to 2n=60.
Chromosome numbers determined in the present study and those reported previously in the family reveal the presence of a continuous series of basic numbers between x=8 and x=34. The commonest basic number in the family is x=16. In view of the low haploid numbers n=8 observed in two genera in the present study, x=16 is presumed to have been derived from the lower x=8 by doubling. According to the present investigation, the number 8 is suggested as the ancestral basic number of the family. It appears that aneuploid changes of chromosome numbers produced the basic numbers of x=11, 13, 14, 15 and 16 in the early evolution of the family, after which polyploidy and dibasic amphidiploidy gave rise to the higher basic numbers (x=17 to 34) now found in the family.
Karyotypes in the family also show differences in absolute chromosome size indicating changes in nuclear DNA in evolution. No definite trend of either phylogenetic increase or decrease of chromosome size is indicated by the available data.