Contributions to cytogenetics of Plectranthus barbatus Andr. (Lamiaceae): a medicinal plant

Abstract. Accessions of Plectranthus barbatus (Lamiaceae), a medicinal plant, were investigated using a cytogenetic approach and flow cytometry (FCM). Here, we describe for the first time details of the karyotype including chromosome morphology, physical mapping of GC rich bands (CMA(3 )banding), as well as the mapping of 45S and 5S rDNA sites. All accessions studied showed karyotypes with 2n = 30 small metacentric and submetacentric chromosomes. The CMA(3) banding and fluorescent in situ hybridization techniques revealed coincidence between CMA(3) bands and 45S rDNA sites (6 terminal marks) while for the 5S rDNA were observed 4 subterminal marks no coincident with CMA(3 )marks. For nuclear genome size measurement, the FCM procedure provided histograms with G(0)/G(1 )peaks exhibiting CV between 2.0–4.9 and the mean values obtained for the species was 2C = 2.78 pg, with AT% = 61.08 and GC% = 38.92. The cytogenetic data obtained here present new and important information which enables the characterization of Plectranthus barbatus.