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Dioecy is a common phenomenon among Atriplex species. However, a mechanism of sex determination has not been determined in this group. We discovered a male-specific RAPD DNA fragment of 2075 bp which was identified with the primer OPAF-14 (5'GGTGCGCACT3') in Atriplex garrettii. The 2075 bp fragment was cloned and sequenced. The DNA sequence of the 2075 bp fragment contains several direct repeats, but no inverted repeats. Two 24-mer oligonucleotype primers which exclusively amplified this fragment were designed and used as SCAR primers. Cytogenetic analysis revealed no apparent heteromorphic chromosome suggesting that sex determination in A. garrettii is genetic, with no evidence of heteromorphic sex chromosomes.

Analysis of chromosome morphology was performed in 23 annual and 31 perennial taxa of Atriplex. The taxa analized were predominantly diploid with 2n = 18 chromosomes. However, tetraploid and hexaploid were also common in both annual and perennial species. While annual Atriplex species were highly variable in their karyotype constitution, perennial species had, comparatively, very uniform chromosome patterns. Differences in chromosome morphology and in haploid chromosome length suggested the presence of interspecific variation for DNA content among annual Atriplex species. Karyotype analysis suggested that perennial Atriplex species have evolved predominantly by centromeric shifts and polyploidy while annual Atriplex species differed by addition and deletion of chromatin associated with structural chromosome changes and polyploidy.

Parapiptadenia rigida is a tropical early secondary succession tree characteristic of the Tropical Atlantic Rainforest. This species is of great ecological importance in the recovery of degraded areas. In this study we investigated the variability and population genetic structure of eight populations of P. rigida. Five AFLP primer combinations were used in a sample of 159 individuals representing these eight populations, rendering a total of 126 polymorphic fragments. The averages of percentage of polymorphic loci, gene diversity, and Shannon index were 60.45%, 0.217, and 0.322, respectively. A significant correlation between the population genetic variability and the population sizes was observed. The genetic variability within populations (72.20%) was higher than between these (22.80%). No perfect correlation was observed between geographic and genetic distances, which might be explained by differences in deforestation intensities that occurred in these areas. A dendrogram constructed by the UPGMA method revealed the formation of two clusters, these also confirmed by Bayesian analysis for the number of K cluster. These results show that it is necessary to develop urgent management strategies for the conservation of certain populations of P. rigida, while other populations still preserve reasonably high levels of genetic variability.