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CHROMOSOME NUMBERS AND POLYPLOIDY IN THE LEGUMES OF PAKISTAN

SURAYYA KHATOON AND SYED IRTIFAQ ALI

Abstract: Original counts of 15 species of leguminous plants of Pakistan are reported here including 3 counts new to science. This brings the total number of chromosomally known leguminous species in the flora of Pakistan to 208 belonging to 68 genera i.e., 40.15% of the total leguminous species in our flora. The incidence of polyploidy is discussed in relation to taxonomic groups, their phylogenetic position, habit classes and phytogeographic regions. The more archaic subfamilies i.e. Caesalpinioideae and Mimosoideae show the retention of higher basic numbers (x=12-14) with secondary cycle of polyploidy non-existent in the former (in our sample) while exhibited by some species like Acacia spp., and Prosopis juliflora in the latter. In Papilionoideae, the comparatively archaic tribes like Sophoreae and Millettieae exhibit higher basic numbers, but more advanced herbaceous tribes have lower basic numbers (x=6-8). In habit classes, woody species show the retention of high basic numbers with little intrageneric polyploidy (1.92%), while the herbaceous and weedy species show lower basic numbers but higher intrageneric polyploidy. The highest percentage of intragenetic polyploidy among various habit types in the sample is met with in annual herbs (3.8%), which are mostly weedy species belonging to the tribes Indigofereae and Trifolieae. The modal basic number in the sample is found to be 8 followed by 11, at the specific as well as at generic level. Basic numbers higher than 11 are most frequent in the Tropico-subtropical phytogeographic elements followed by Sino-Japanese and Indian elements. The intrageneric polyploids of Papilionoideae do not show any obvious correlation with any phytogeographic region. The overall percentage of intrageneric polyploidy in the sample is found to be 10.096% (0% in Caesalpinoideae, 26.6% in Mimosoideae, 10.1% in Papilionoideae). It is somewhat lower than the world average for the family Leguminosae.

Department of Botany, University of Karachi, Karachi-75270, Pakistan.