Phylogenetic and Biogeographic Analysis in Myrcia Sect. Myrcia (Myrcia s.l., Myrtaceae) with Focus on Highly Polyphyletic Myrcia splendens

Abstract

Premise of research. Myrcia s.l. is the largest exclusively Neotropical genus of Myrtaceae, comprising about 800 species. This large genus is divided into 10 clades, most of these recently published as sections. One section, Myrcia sect. Myrcia, has 114 species distributed from Mexico to Uruguay, with species diversity centers in the Atlantic Forest, Amazon, and Cerrado. This section includes one of the most difficult to circumscribe species of the Neotropical flora, Myrcia splendens, with the same distribution as the genus and currently with almost 170 synonyms. Phylogenetic relationships and biogeographic patterns in Myrcia sect. Myrcia are examined for the first time using molecular data. Methodology. Phylogenetic inference is based on maximum likelihood and Bayesian analysis of internal transcribed spacer (nuclear), ndhF, psbA-trnH, trnL-trnF, and trnQ-rps16 (plastid) sequences obtained by sequencing a morphologically and geographically representative sample. Phylogenetic relationships, divergence time estimates, and biogeographic patterns are investigated using BEAST and BioGeoBEARS. Pivotal results. Results show that Myrcia sect. Myrcia is monophyletic as morphologically circumscribed. Internal relationships indicate morphologically distinct lineages, but the widespread and taxonomically unruly M. splendens emerges as polyphyletic. Lineages from Central America and the Amazon are sister to multiple dispersals to disparate biomes and subsequent colonization of the Cerrado. Further field and laboratory studies are necessary to understand the extreme morphological plasticity of this section, with a particular focus on improving taxonomic delimitations in M. splendens. Conclusions. This article represents the largest sample of Myrcia sect. Myrcia examined to date. The results presented here demonstrate the monophyly of the section and confirm the nonmonophyly of the widespread M. splendens, with multiple accessions emerging in independent clades from different biomes. The mean estimated age for Myrcia sect. Myrcia is 22.4 mya, and the four clades of focus in this article are estimated to have originated in the Miocene.