Systematic studies in Neotropical Myrtaceae with an emphasis on Myrcia s.l.: The evolution and biogeography of a large South American clade

Lucas, E.J. (2007). Systematic studies in Neotropical Myrtaceae with an emphasis on Myrcia s.l.: The evolution and biogeography of a large South American clade. PhD thesis The Open University.

DOI: https://doi.org/10.21954/ou.ro.0000ea36

Abstract

Low morphological variation at all taxonomic levels give Neotropical Myrtaceae a reputation as a 'difficult' family to identify even to genus, resulting in a lack of taxonomic data on every front. The subtribal classification of the predominantly Neotropical and exclusively fleshy-fruited tribe Myrteae (49 genera and c. 2500 species) is unstable, as are generic boundaries within it. Neotropical Myrtaceae are particularly species rich in some of South America's most threatened habitats. The second largest Neotropical genus, Myrcia s.l., comprises >700 taxonomically 'difficult' species with species diversity reaching its peak in the Brazilian Atlantic rainforest and cerrado, habitats in urgent need of inventories of their plant species before conservation initiatives can be undertaken.

Phylogenetic hypotheses are provided for evolutionary relationships within Myrteae and Myrcia s.l. based on nuclear ITS and ETS ribosomal DNA and plastid psbA-trnH and matK DNA sequences, using parsimony and Bayesian inference. Four morphological characters of Myrteae are optimized on the resulting trees and nineteen are used in a cladistic analysis of Myrcia s.l. Myrteae appear monophyletic, comprising seven clades plus two isolated taxa. Of the four previously accepted genera of subtribe Myrciinae sensu DC., two are polyphyletic and all emerge in a single clade treated here as Myrcia s.l. Morphological characters exhibit homoplasy at both ranks, although in combination are useful for clade diagnosis.

Biogeographical analysis is inconclusive regarding tribal ancestral areas, but South American colonization before northern radiation via the Andes appears likely. The largest genera, Eugenia and Myrcia s.l., have western and southeastern South American origins, respectively. Nonmetric multidimensional scaling and ordination techniques are employed to divide the distribution of Myrcia s.l. into discrete areas of endemism and historical biogeographical scenarios are discussed. Finally, modern, natural, subtribal and infrageneric classifications are proposed and concluding inferences are drawn regarding drivers of large genera using Myrtaceae and Myrcia s.l. as case studies.