Abstract
Cytogenetic studies on the Sida rhombifolia complex in Nigeria were carried out using plant material from most of the range of the species. Chromosome number of 2n=14 for the two diploid subspecies (subsp. rhombifolia and subsp. retusa) and 2n=28 for the tetraploid subspecies (subsp. alnifolia) were obtained. The micro-morphological features (e. g. stomata and pollen grains) of the tetraploid plants were more in size than in the diploid plants. Only crosses between the two diploid subspecies set viable seeds. The hybrid plants were vigorous and generally intermediate morphologically between the two parents in many respects. Pollen stainability was less than 50% in F1 hybrids.
