In the present study, the chromosomes numbers were confirmed, 2n = 34 for Amaranthus cruentus Linnaeus, 1759, and 2n = 32 for Amaranthus hypochondriacus Linnaeus, 1753, Amaranthus mantegazzianus Passer, 1864, and Amaranthus caudatus Linnaeus, 1753. The distribution and variability of constitutive heterochromatin were detailed using DAPI-CMA3 banding technique. The position of the nucleolus organizer region (NOR) was observed using Ag-NOR banding (active loci) and fluorescent in situ hybridization (rDNA-FISH) in the four Amaranthus species. Variations in the amount of constitutive heterochromatin were detected both within the species and between them, with DAPI-CMA3 stain. One chromosome pair having a NOR was found in each studied accession, with exception of Amaranthus caudatus cv. EEA INTA Anguil. This accession presented four rDNA loci (FISH), being active two of them (Ag- banding).

Paspalum schesslii, a new species from the state of Mato Grosso in central-western Brazil, is described and illustrated. The new species is related to P. malmeanum, from central-western Brazil and eastern Bolivia, and Paspalum eucomum, from central Brazil. It comprises shorter plants with leaf blades and racemes shorter than those of the related species, and spikelets having obovate, deciduous upper florets. An unexpected chromosome number 2n = 12 was found in specimens of P. schesslii; thus it differs from both P. malmeanum, which has 2n = 20, and P. eucomum, for which 2n = 30 and 2n = 32 chromosome counts are here reported for the first time. The discovery of a new species having 2n = 12, which often cohabits with diploid populations of the widespread related species, P. stellatum, is consistent with an hypothesis about the hybrid origin of the polyploid cytotypes of P. stellatum having 2n = 32 and 2n = 52 chromosomes. Moreover, such an hybrid origin involving parental species with different base chromosome numbers (x = 6 and x = 10) could also explain the occurrence of 32 chromosomes in P. eucomum, potentially documenting a speciation mechanism that is otherwise unknown in the genus.

Oxalis lacinata is endemic to the Patagonia region, including high mountains and steppe, and even grows on the coast. Its marked polymorphism made us think that the genetic variability behind this would explain both its morphological variability and its adaptability to different ecological niches. Based on molecular analysis, we detected non-random organization of genetic variability. We propose two refugia and we were able to estimate the diversification centre, which coincides with the centre of the distribution. Distribution modelling suggested the possibility of occurrence in the Central Andes, in addition to its known distribution.

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