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Phylogeny of Subtribe Myrciinae (Myrtaceae)

Variation in Myrcia flowers. © Eve Lucas

The most commonly cited previous classification of tribe Myrteae sensu Wilson et al (2005) is the three subtribes of Berg (1855-56) based on embryo characters. The core genera of the subtribe; Myrcia, Marlierea, Gomidesia and Calyptranthes have unique inflorescence and ovary arrangements. Myrceugenia and Luma differ in these latter arrangements but have intermittently been included in Myrciinae due to resemblances of the embryo. Molecular systematic work carried out at Kew has revealed that these core genera comprise a monophyletic group while Myrceugenia and Luma are associated in a distantly related clade.

Myrtaceae are the most important family in terms of tree species in the Brazilian Atlantic forest and cerrado; in these regions, Myrciinae is the most speciose subtribe. The four core genera of the subtribe show all the characteristics that give Neotropical Myrtaceae their reputation as taxonomically ‘difficult’; levels of morphological variation and taxonomic inflation are high and both generic and specific boundaries are blurred.  Species diversity in Myrciinae genera peak in the Brazilian Atlantic rainforest and cerrado (Myrcia, Marlierea, Gomidesia), the Amazon (Marlierea) and the Caribbean (Calyptranthes), habitats disappearing rapidly under human pressure. Revision of the core Myrciinae genera is an essential part of work towards the taxonomic revision of the family, urgently required as Myrtaceae habitats are disappearing at an unprecedented rate.

The main objectives of the Myrciinae phylogeny project are (1) to clarify generic relationships within the subtribe and (2) to provide a reclassification of the Myrciinae based on the new phylogeny and on which future monographic work can be based.  Between 2001-2005, c.80 species of the four Myrciinae genera have been sequenced for the gene regions ITS, ETS, psbA-trnH and matK , of which c. 60 form part of the Myrteae phylogeny and an additional c. 20 have been sequenced as part of part of a PhD study on Marlierea at the University of Campinas (Brazil). Results indicate that Gomidesia and Calyptranthes are monophyletic groups nested within a larger Myrcia s.l. clade.  Myrcia and Marlierea are paraphyletic, with a mixed clade of these latter genera sister to a clade comprising representatives of all four genera.

Morphological studies in subtribe Myrciinae are being carried out in parallel to molecular research. A survey is currently being undertaken to find morphological characters suitable for cladistic analysis alongside the molecular data to support and interpret the resulting arrangement. This project is closely tied to the ‘Myrciinae Biogeography and Conservation’ project which will identify biogeographical areas of endemism with which the resulting phylogeny can be subjected to biogeographical analysis using a variety of methodologies.

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