2003 年 68 巻 1 号 p. 25-30
Three Sida spp. viz. S. acuta, S. rhombifolia var. rhomboidea, S. cordata and a putative hybrid between S. acuta and S. rhombifolia var. rhomboidea were cytogenetically investigated to elucidate their characteristic karyotypes. S. acuta and S. rhombifolia var. rhomboidea possessed 2n=28 and 2n=14 chromosomes, respectively. In S. cordata, 2n=32 and in the putative hybrid, 2n=28 chromosomes were observed. The total length of 2n chromosome complements in S. acuta and S. rhombifolia var. rhomboidea were 55.6 μm, and 35.7 μm, respectively. In S. cordata, total length of 2n chromosome complement was 47.4 μm and in the putative hybrid, 96.7 μm. Except the putative hybrid, all species had only metacentric chromosomes. On the other hand, the putative hybrid had 6 sub-metacentric (6 sm) and 22 metacentric (22 m) chromosomes. Four CMA-positive bands were found in S. acuta, S. cordata and the putative hybrid, whereas, 2 such bands occurred in S. rhombifolia var. rhomboidea. These banded regions were DAPI-negative, indicating their absolute GC-rich nature. Both DAPI-positive (9) and negative (4) bands were found in S. cordata. An analysis of these data indicates that each Sida species possesses a distinct karyotype. The different 2n chromosome number, centromeric formula, length of total chromosome complements and fluorescent banding pattern unequivocally indicate a separate taxonomic rank of the putative hybrid.
