Cytotaxonomical Studies in the Genus <I>Setcreasea</I>

Abstract

Cytological studies have been done in two species of Setcreasea. In Setcreasm purpurea a somatic chromosome number of 12 has been observed and in S. brevifolia an aneuploid number of 2n = 25 has been found. Three major types of chromosomes have been observed m the karyotypes of both taxa. The cytological situation in the two taxa has been observed to, be similar to that of Tradescantia. Meiotic behaviour in S. purpurea is regular while in S. brevifolia it is irregular. The irregularity in the latter taxon is doubtless connected with aneuploidy and structural hybridity. The finding of diploid pollen grains in S. purpurea and S. brevifoliacould have been due to the failure of the chromosomes or chromatids to go to different poles, disturbance in spindle formation, or possibly to a complete failure of cell wall development. Many cases have been found of abnormal cvtokinesis in pollen grain formation. Polyploidy, structural hybridity and hybridization has been considered to be playing major role in evolutionary tendencies in Setcreasea.In view of the cytological and morphological characteristics, it has been suggested that the genus is related to Zebrina and its relationship with Cyanotis is remote. Taking all these factors into consideration, it appears that Setcreasea will be in more natural systematic position if separated widely from Cyanotis and placed near Zebrina.