Phylogeny, biogeography and foliar manganese accumulation of Gossia (Myrtaceae)

© 2018 CSIRO. The rainforest genus Gossia N.Snow & Guymer (Myrtaceae) occurs in Australia, Melanesia and Malesia, and is capable of hyperaccumulating the heavy metal manganese (Mn). Here, we used nuclear ribosomal and plastid spacer DNA-sequence data to reconstruct the phylogeny of 19 Australian species of Gossia and eight New Caledonian taxa. Our results indicated that the relationship between Gossia and Austromyrtus (Nied.) Burret is not fully resolved, and most Australian species were supported as monophyletic. Non-monophyly might be related to incomplete lineage sorting or inaccurate taxonomic classification. Bark type appears to be a morphological synapomorphy separating two groups of species, with more recently derived lineages having smooth and mottled 'python' bark. New Caledonian species were well resolved in a single clade, but were not the first diverging Gossia lineage, calling into doubt the results of a recent study that found Zealandia as the ancestral area of tribe Myrteae. Within Australia, the evolution of multiple clades has probably been driven by well-known biogeographic barriers. Some species with more widespread distributions have been able to cross these barriers by having a wide range of soil-substrate tolerances. Novel Mn-hyperaccumulating species were identified, and, although Mn hyperaccumulation was not strongly correlated with phylogenetic position, there appeared to be some difference in accumulation levels among clades. Our study is the first detailed phylogenetic investigation of Gossia and will serve as a reference for future studies seeking to understand the origin and extent of hyperaccumulation within the Myrteae and Myrtaceae more broadly.