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Phylogeny and systematics of Schinus L. (Anacardiaceae), with revision of a clade endemic to the Andean cloud forests

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Author(s):
Cintia Luiza da Silva Luz
Total Authors: 1
Document type: Doctoral Thesis
Press: São Paulo.
Institution: Universidade de São Paulo (USP). Instituto de Biociências (IBIOC/SB)
Defense date:
Examining board members:
Jose Rubens Pirani; Maria Fernanda Aguiar Calió; Rubens Luiz Gayoso Coelho; Milton Groppo Junior; Jefferson Prado
Advisor: Jose Rubens Pirani
Abstract

Schinus, a genus best known by its few cultivated and invasive species, is the largest genus of Anacardiaceae in southern South America. It is remarkably diverse compared to closely related genera, with approximately 42 species, most of which occur in several arid vegetation types and extending into Andean and Atlantic moist forests. The most comprehensive taxonomic revision of the genus dates to 1957, which recognized S. subg. Schinus and S. subg. Duvaua, the latter of which was further divided into two sections. Subsequent studies have highlighted morphological inconsistencies in this infrageneric classification, and species delimitation remains a challenge. Schinus has been poorly sampled in previous phylogenetic studies of Anacardiaceae, and thus any assumptions about its monophyly and relationships (particularly among its species and infrageneric categories) remain untested. This thesis aimed to test the monophyly of Schinus and its infrageneric circumscriptions, and also investigate the phylogenetic relationships. In the first chapter, we present the phylogenetic relationships of all Schinus species using nine nuclear and two plastid DNA sequence regions, most of them developed recently for Commiphora (Burseraceae). The maximum parsimony, maximum likelihood, and Bayesian inference included 47 taxa based on the latest taxonomic revision of the genus, and 48 specimens of Anacardiaceae genera closely related to Schinus. We also constructed a morphological dataset, including vegetative anatomical features, based on analysis of herbarium specimens and fresh material obtained through fieldwork, and compared these characters to hypotheses based on molecular evidence in order to: 1. achieve a better understanding of the relationships among its species and to related genera, 2. identify morphological characters and putative synapomorphies for major clades, and 3. discuss hypotheses regarding the evolution of structural traits in the group. Our analyses strongly support the monophyly of Schinus, but also indicate that its infrageneric groups S. subg. Duvaua sect. Duvaua and S. subg. Duvaua sect. Pseudoduvaua are polyphyletic and have been defined using homoplastic characters. The phylogenetic relationships that emerged from our analyses include eight strongly supported lineages (except for S. sect. Atlantica), in which compound-leaved taxa were the earliest diverging lineages, forming a grade of three strongly supported clades, and the largest Schinus clade consists of simple-leaved species, and has five well-supported main lineages. However the relationships among closely related species remain unclear in some clades. Ancestral state reconstructions demonstrate that some morphological and leaf-anatomical characters are valuable in characterizing some lineages, and may serve as potential synapomorphies to define these clades. By contrast, most of the traits that have traditionally been used to circumscribe groups in Schinus show high levels of homoplasy. In light of these results, we present in the first chapter a novel sectional classification of Schinus, an identification key for the sections and comments on the taxonomy, geographic distribution and ecology. The eight monophyletic sections proposed here are recognized by a combination of character states associated with geographic distribution, corresponding to lineages that are mostly allopatric or at least ecologically distinct. This study is the first phase of a long-term effort to produce systematics studies and taxonomic review for all species of Schinus. In this way, we present in the second chapter the taxonomic revision of S. sect. Myrtifolia, a remarkable simple-leaved clade in which species reach the highest elevations within Anacardiaceae (up to 3,900 m altitude). The 11 species of this section are mostly endemic of Yungas and Tucumán-Bolivian forests, and two species also occur in pre-Puna, Puna and dry inter-Andean valleys from Argentina, Bolivia and Peru. The fact that most of the morphological traits present high levels of homoplasy, the diagnosis of the main clades within Schinus is a challenge, except for S. sect. Myrtifolia whose species have tetramerous flowers and fruits laterally compressed, unusual character states that seem to be putative synapomorphies of this section. Its members were previously placed in S. subg. Duvaua sect. Pseudoduvaua, except for S. microphylla, a species recognized as belonging to S. subg. Duvaua sect. Duvaua. Delimitation issues have been neglected in species of this section, since most studies have focused on taxa belonging to S. subg. Duvaua sect. Duvaua. The present morphological study reveals a significant number of taxonomic circumscription problems, especially between S. andina and S. myrtifolia. Detailed morphological analyses of numerous exsiccatae reveals four new species which are described herein. We provide identification key, descriptions, synonyms, nomenclatural types, including three designations of lectotypes, two new combinations, illustrations, distribution maps, and comments on nomenclatural, distribution and preliminary conservation assessments of all species. The taxonomic novelties here presented in Schinus sect. Myrtifolia contribute to disentangle the complexity of the group and its misidentified species, taking into account the morphological traits of a virtually complete sampling and a careful nomenclatural revision. In this way we hope to have evaluated all range of morphological variation, especially within S. andina and S. myrtifolia, which has been overlooked until now. In summary the phylogenetic study of Schinus provided here including a much broader sampling of all lineages in the genus, offers opportunities for further taxonomic, evolutionary and biogeographical studies in Schinus. The biogeographical investigations associated with the diversification of Schinus and closely related taxa from Anacardiaceae seem to be promising and may contribute to new insights into the history of southern South American biota (AU)

FAPESP's process: 13/04345-2 - Systematic and biogeography of Schinus L. (Anacardiaceae)
Grantee:Cíntia Luíza da Silva Luz
Support type: Scholarships in Brazil - Doctorate