Plectranthus is a genus which includes species of ornamental and medicinal potential. It faces taxonomic problems due to aggregating species previously belonging to the genus Coleus, a fact that has contributed to the existence of various synonymies. The species Plectranthus
amboinicus, Plectranthus
barbatus, Plectranthus
grandis and Plectranthus
neochilus are included in this context. Some authors consider Plectranthus
barbatus and Plectranthus
grandis as synonyms. The present work was carried out with the aim of comparing plants of the above-mentioned species, originating from different localities in Brazil, with regards to chromosome number and karyotypic morphology, correlated to the nuclear DNA content. There was no variation in chromosome number among plants of the same species. Plectranthus
amboinicus was the only species to exhibit 2n=34, whereas the others had 2n=30. No karyotypic differences were found among the plants of each species, except for Plectranthus
barbatus. The plants of the Plectranthus species revealed little coincidence between chromosome pairs. The nuclear DNA content allowed grouping Plectranthus
amboinicus and Plectranthus
neochilus, with the highest mean values, and Plectranthus
grandis and Plectranthus
barbatus with the lowest ones. Differences in DNA amount among the plants were identified only for Plectranthus
barbatus. These results allow the inference that the populations of Plectranthus
amboinicus and Plectranthus
neochilus present coincident karyotypes among their plants, and Plectranthus
grandis is probably a synonym of Plectranthus
barbatus.