Quantitative delineation of karyotype variation in Papaver as a measure of phylogenetic differentiation and origin

Karyomorphology of 30 species of Papaver L. (Papaveraceae) and in situ localization of rDNA sites on chromosomes of P. somniferum was used to establish phylogenetic affinities, ancestry and chromosomal variation during speciation. A simple biometrical parameter, the ‘Dispersion Index’, was employed to facilitate quantitative evolutionary gradation between the closely related karyotypes that fall under the same class of karyotypic asymmetry. The karyoevolutionary data thus obtained is combined with the morphotaxonomic information to project species interrelationships and probable phylogenetic order. Over 2-fold diminution in relative chromosome size is associated with speciation in this genus. Diminution is almost uniform except the smallest pair. The degree of reduction in the short arm is proportionately more than that in the long arm. The opium poppy, Papaver somniferum (2n = 22), a deviation from x = 7, appears to have originated via chromosomal introgression through aneuallopolyploidy involving addition of nucleolar chromosomes from two or more species. Possibly, a progenitor triploid hybrid between species like P. glaucum (2n = 14) and P. gracile (2n = 28) may have preceded the speciation of P. setigerum (2n = 22) and P. somniferum (2n = 22) in concurrent succession.