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Phylogeny and karyology of Psidium and Campomanesia - COMPLETED

Molecular systematics of Psidium and Campomansia, including genome size evolution.


Laura Jennings
Psidium guajava

With ca. 100 species, Psidium (Myrtaceae) is an important component of Neotropical flora and widespread in the Brazilian Cerrado and Tropical Atlantic Rain Forest. This is a highly taxonomically complex genus and some natural hybridization cases have been identified. Recent phylogenetic studies indicate Psidium to be a monophyletic taxon, although relatively small taxonomic sampling leaves delimitation of some species unclear. To help assist taxonomic delimitation and understanding of species and capitalizing on previous experience in Myrtaceae molecular systematic projects carried out at Kew, collaborating researchers from Kew and Brazil (notably the Federal University of Ceará) are applying different methodologies to assess the evolutionary history of Psidium and the closely related genus Campomanesia.

These protocols include: phylogenetic analysis based on molecular data and chromosomal and genome size studies in an evolutionary context. Phylogenetic analysis was based on the ‘Pimenta group’ hypothesized by the latest phylogeny of Myrteae carried out at Kew, but supplemented this study with greater taxonomic and geographical sampling from species collected in the Amazonia, Brazilian Cerrado, Caatinga and Tropical Atlantic Rain Forest biomes. It has become apparent that both Psidium and Campomanesia species demonstrate clear biogeographical pattern. With species from different biomes emerging in well supported clades.

The chromosomal approach includes the majority of taxa sampled in the phylogenetic analysis. All species present small chromosomes (<2µm). The diploid chromosome number 2n=2x=22 occurred in these genera, exception for Psidium, where this number was observed in only two species (P. guajava and P. guineense). Polyploidy was observed in 82% of species of Psidium with a big variation on the ploidy levels (2n=22, 44, 55, 66, 88). The distribution and number of rDNA 45S sites suggest a hybrid origin of the hexaploid.

The genome size (2C-values) was determined by flow cytometry for 10 species of Psidium. The intra-specific variation of 2C-value was 9-fold, in a positive correlation with ploidy level. Future collaborative studies will increase the sampling of molecular and chromosomal data to clarify species relationships and biogeographical patterns in Psidium and to explain origins of polyploidy in differing environments.

Project partners and collaborators


Federal University of Ceará

Project funders


REFLORA (CNPq, Rio de Janeiro Botanic Gardens, Natura)

Project Department