The genusSmilaxLinnaeus, 1753 (Smilacaceae) is a large genus of dioecious plants distributed in tropical, subtropical and temperate regions. SomeSmilaxspecies have medicinal importance and their identification is important for the control of raw material used in the manufacture of phytotherapeutical products. The karyotypes of seven BrazilianSmilaxspecies were investigated. Mitotic metaphases of roots from young plants were analysed in Feulgen-stained preparations. The karyotypes were asymmetric and modal with 2n = 2x = 32 chromosomes gradually decreasing in size. InS. goyazanaA De Candolle & C De Candolle, 1878, a polyploid species, 2n = 4x = 64. In all the species, the large and medium-sized chromosomes were subtelocentric and submetacentric and the small chromosomes were submetacentric or metacentric. Their karyotypes were quite similar, with differences in the arm ratio of some chromosomes.S. fluminensisSteudel, 1841 differed from the other species by having a large metacentric chromosome 1. These findings suggest that evolution occurred without drastic changes in the chromosomal structure in the species analyzed. Terminal secondary constrictions were visualized on the short arm of some chromosomes, but they were detected only in one homologue of each pair. Due to the terminal location and the degree of chromosome condensation, secondary constrictions were not visualized in some species. The nucleolus organizer regions (NORs) were mapped by silver-staining and fluorescentin situhybridization (FISH) inS. rufescensGrisebach, 1842 andS. fluminensis. Silver-staining and FISH signals were colocalized on the short arms of six chromosomes inS. rufescensand four chromosomes inS. fluminensis. In FISH preparations, one of the largest chromosomes had the secondary constrictions highly decondensed in some cells. This finding and the heteromorphism observed in Feulgen-stained chromosomes suggest that differential rRNA gene expression between homologous rDNA loci can occur in some cells, resulting in different degrees of ribosomal chromatin decondensation. The presence of a heteromorphic chromosome pair inS. rufescens,S. polyanthaGrisebach, 1842 andS. goyazanasuggests a chromosomal sex determination in these dioecious species.
