Cytological studies on south Indian araceae.

Abstract

Cytology of 30 species (including several varieties) coming under 17 genera of the Araceae, mostly from South India has been studied. Chromosome numbers determined in the present study range from 2n=16 to 2n=112.Meiotic studies of 11 species and some varieties have been made. Caladium bicolor showed chromatid bridges and fragments at anaphase I. The tetraploid race of Typhonium divaricatum formed six to nine rings of four chromosomes at diakinesis. Pentaploid race of this species showed chains of five chromosomes and rings of four. Meiosis was largely regular in the other species studied. Aberrations in microsporogenesis reported previously in diploid Colocasia antiquorum have not been found in plants of this species examined in the present study. Diploids of C. antiquorum and C. esculenta showed regular meiosis and seed formation. The embryos which abort under natural conditions have been grown in culture medium.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=18. However, 22 out of 50 genera known cytologically so far have chromosome numbers in multiples of 14. In view of the low haploid numbers n=8 observed in two genera, x=14 is presumed to have been derived from the lower x=7 by doubling. The number 7 is suggested as the ancestral basic number of the family. It appears that aneuploid changes of chromosome numbers produced basic numbers of x=6, 7, 8, 9 and 10 in the early evolution of the family, after which polyploidy and dibasic amphidiploidy gave rise to the higher basic numbers (x=12 to 18) 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. Reduction in size of chromosomes appears to have been an adaptation to an aquatic habitat in some genera.