Morphological homogeneity, phylogenetic heterogeneity and systematic complexity in species-rich groups: a case study of floral evolution in Myrteae (Myrtaceae)

Myrteae is the most diverse tribe in the species-rich angiosperm family Myrtaceae. Myrteae species play a critical ecological role in tropical forests and savannas, biomes with some of the highest biodiversity on earth. Hence there is a growing interest in its use as a model for evolutionary, ecological and conservation studies. However, morphologically homogeneous reproductive structures cause taxonomic instability and jeopardize modelling and conservation initiatives. This study demonstrates how evolutionary patterns are underpinned by floral traits in Myrteae. Aims are approached using combined phylogenetic and morphological analyses in two work packages (WP): WP1 increases understanding of systematics and floral evolution in Myrteae based on multiloci molecular matrices for a near complete generic sample. The framework is used to interpret biogeography, diversification and over-arching patterns of floral morphology and development; data are reciprocally combined to illuminate those processes. WP2 presents four case studies using floral development and multidimensional trait analysis to address questions related to systematic complexity, phylogenetic heterogeneity and theoretical cladistics concepts, such as evolution of homoplastic traits. Results harness Myrteae as a model group to address relevant questions in plant evolution and systematics; the applicability of this approach to similar questions in other diverse tropical angiosperm groups is discussed

Nomenclatural and taxonomic changes in tribe Myrteae (Myrtaceae) spurred by molecular phylogenies

Phylogenetic studies have highlighted incongruous generic placement and the usage of inappropriate names for species within tribe Myrteae (Myrtaceae). The genera affected are Calycolpus, Eugenia, Myrcia and Psidium. Eugenia aubletiana is legitimized by the designation of a lectotype and its usage proposed instead of Calycorectes bergii. Two generic transfers are proposed: Psidium sessiliflorum based on Calycolpus sessiliflorus and Myrcia neosericea, based on Eugenia neosericea. The re-instatement of Psidium cupreum, currently a synonym of Psidium rufum as an accepted species is proposed. Illustrations of the four affected species are furnished, as well as a map of occurrences of Psidium sessiliflorum. Tetramery associated to inflorescences reduced to 1(-3) flowers, an unusual combination of characters in Myrcia sect. Gomidesia, is identified in both Myrcia glaziovii and Myrcia neosericea, and a key to distinguish them is provided

Fast diversification through a mosaic of evolutionary histories characterizes the endemic flora of ancient Neotropical mountains

Mountains are among the most biodiverse areas on the globe. In young mountain ranges, exceptional plant species richness is often associated with recent and rapid radiations linked to the mountain uplift itself. In ancient mountains, however, orogeny vastly precedes the evolution of vascular plants, so species richness has been explained by species accumulation during long periods of low extinction rates. Here we evaluate these assumptions by analysing plant diversification dynamics in the campo rupestre, an ecosystem associated with pre-Cambrian mountaintops and highlands of eastern South America, areas where plant species richness and endemism are among the highest in the world. Analyses of 15 angiosperm clades show that radiations of endemics exhibit fastest rates of diversification during the last 5 Myr, a climatically unstable period. However, results from ancestral range estimations using different models disagree on the age of the earliest in situ speciation events and point to a complex floristic assembly. There is a general trend for higher diversification rates associated with these areas, but endemism may also increase or reduce extinction rates, depending on the group. Montane habitats, regardless of their geological age, may lead to boosts in speciation rates by accelerating population isolation in archipelago-like systems, circumstances that can also result in higher extinction rates and fast species turnover, misleading the age estimates of endemic lineages

Nomenclatural and taxonomic changes in tribe Myrteae (Myrtaceae) spurred by molecular phylogenies

Phylogenetic studies have highlighted incongruous generic placement and the usage of inappropriate names for species within tribe Myrteae (Myrtaceae). The genera affected are Calycolpus, Eugenia, Myrcia and Psidium. Eugenia aubletiana is legitimized by the designation of a lectotype and its usage proposed instead of Calycorectes bergii. Two generic transfers are proposed: Psidium sessiliflorum based on Calycolpus sessiliflorus and Myrcia neosericea, based on Eugenia neosericea. The re-instatement of Psidium cupreum, currently a synonym of Psidium rufum as an accepted species is proposed. Illustrations of the four affected species are furnished, as well as a map of occurrences of Psidium sessiliflorum. Tetramery associated to inflorescences reduced to 1(-3) flowers, an unusual combination of characters in Myrcia sect. Gomidesia, is identified in both Myrcia glaziovii and Myrcia neosericea, and a key to distinguish them is provided

Diversity, phylogeny and evolution of the rapidly evolving genus Psidium L. (Myrtaceae, Myrteae).

BACKGROUND AND AIMS: Psidium is the fourthth largest genus of Myrtaceae in the Neotropics. Psidium guajava is widely cultivated in the tropics for its edible fruit. It is commercially under threat due to the disease guava decline. Psidium cattleyanum is one of the 100 most invasive organisms in the world. Knowledge of the phylogenetic relationships within Psidium is poor. We aim to provide a review of the biology, morphology and ecology of Psidium, a phylogenetic tree, an infrageneric classification and a list of species. METHODS: Morphological and geographic data were obtained by studying Psidium in herbaria and in the field between 1988 and 2020. Forty-six herbaria were visited personally. A database of approx. 6000 specimens was constructed, and the literature was reviewed. Thirty species (about a third of the species in the genus) were sampled for molecular phylogenetic inference. Two chloroplast (psbA–trnH and ndhF) and two nuclear (external transcribed spacer and internal transcribed spacer) regions were targeted. Phylogenetic trees were constructed using maximum likelihood (ML; RaxML) and Bayesian inference (BI; MrBayes). KEY RESULTS: Psidium is a monophyletic genus with four major clades recognized as sections. Section Psidium (ten species), to which P. guajava belongs, is sister to the rest of the genus; it is widespread across the Neotropics. Section Obversifolia (six species; restricted to the Brazilian Atlantic Forest), which includes P. cattleyanum, is sister to the innermost clade composed of sister sections Apertiflora (31 species; widespread but most diverse in the Brazilian Atlantic Forest) + Mitranthes (26 species; widespread in dry forests and probably diverse in the Caribbean). Characters associated with diversification within Psidium are discussed. CONCLUSIONS: Research on pre-foliation, colleters, leaf anatomy, leaf physiology, staminal development, placentation and germination associated with the anatomy of the opercular plug is desirable. Studies are biased towards sections Psidium and Obversifolia, with other sections poorly known