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Bose, Smritimoy
- Cytotaxonomical Studies in the Genus Setcreasea
Authors
1 Cytogenetics Laboratory, Department of Botany, Calcutta University, Calcutta-19, IN
Source
Nelumbo - The Bulletin of the Botanical Survey of India, Vol 4, No 1-4 (1962), Pagination: 17-26Abstract
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.
- Cytotaxonomy of Amaryllidaceae
Authors
1 Cytogenetics Laboratory, Department of Botany, Calcutta University, Calcutta-19, IN
Source
Nelumbo - The Bulletin of the Botanical Survey of India, Vol 4, No 1-4 (1962), Pagination: 27-38Abstract
Chromosome numbers are now known for about 46 genera in the family Amaryllidaceae. The lowest basic number has been found to be 5 and the' highest 30. Besides these two, 6, 7, 8, 9, 10, 11, 12, 14, 15, 16, 19, 23 and 29 have also been encountered of which 11 is found in majority of the genera. In a number of genera the derivation of one basic number from the other has been established. In the genus Allium largest number of species have been studied cytologically. The next largest is Narcissus followed by Zephyranthes, Crinum, Hippeastrum and Lycorisin that order.B or supernumerary chromosomes have been observed in Agapanthus, Allium, Crinum, Cooperia, Haemanthus, Hippeastrum, Lycoris and Narcissus.
In this family repatterning of chromosomes through inversions (both para afid pericentric), translocation, polyploidy (eu-, aneuo-, hetero-, auto-, and allopolyploidy) and hybridization have played prominent role in chromosome number evolution, karyotype alteration and specisvtion. In addition to this, gene mutation has also played significant part in speciation. Ready vegetative propagation has helped in maintaining sterile hybrids and those forms with numerical and structural changes of chromosomes. Apomixis has also been responsible in chromosome number evolution in some genera.
A consideration of taxonomic work done in Amaryllidaceae points out that Hutchinson's system of classification, based on the umbellate inflorescence rather than on the position of the ovary, has been found to be more phylogenetic but the amendments proposed by several workers for changes in tribal and generic level could be taken into consideration and in some cases may be justified.