Seed Diversity in the Tribe Miconieae (Melastomataceae): Taxonomic, Systematic, and Evolutionary Implications

and Evolutionary Implications. PLoS ONE 9(6): e100561. doi:10.1371/journal.pone.0100561 Seed Diversity in the Tribe Miconieae (Melastomataceae): Taxonomic, Systematic, and Evolutionary Implications Gilberto Ocampo 0 Fabia n A. Michelangeli 0 Frank Almeda 0 Zhong-Jian Liu, The National Orchid Conservation Center of China; The Orchid Conservation & Research Center of Shenzhen, China 0 1 California Academy of Sciences, Institute for Biodiversity Science and Sustainability, Department of Botany , San Francisco , California, United States of America , 2 The New York Botanical Garden, Bronx, New York , United States of America Miconieae is the largest tribe in the Melastomataceae with over 1,850 species. The members of Miconieae display a wide range of morphological diversity, and seed morphology is no exception. Previous studies have found that seed morphological diversity is not congruent with traditional classifications, and suggest that it may reflect evolutionary relationships within Miconieae. Here we characterize seed morphology of 364 species of Miconieae. The morphological data set and a DNA sequence data matrix were analyzed under a parsimony and Bayesian framework. Seed characters were used to test taxonomic and clade hypotheses, to estimate morphological ancestral character states, and to assess phylogenetic signal. The phylogenetic analyses of morphological data retrieved a poorly-resolved, low-supported phylogeny; in contrast, a relatively strongly supported phylogeny was estimated using the molecular data. Hypothesis testing procedures could only reject the monophyly of Clidemia, Leandra, and Miconia. The results indicated that the seed morphological characters were homoplasious, but contained phylogenetic signal. The morphological seed types that were described in previous studies did not support any of the clades retrieved by the molecular phylogeny. In contrast with previous investigations, our study shows that although seed morphology is very variable, it does not provide information for supporting some genera or clades within Miconieae. However, it is suggested that seed characters in combination with other vegetative and reproductive traits may aid in the characterization of smaller clades. The presence of phylogenetic signal retrieved by homoplasious characters may indicate that diversification of seed characters could have an adaptive component. Further studies that increase taxon sampling, refine seed trait characterization, and evaluate the alleged relationships between environmental variables and seed diversification will contribute to a better understanding of seed morphology and evolution in this species-rich tribe. - Seed morphology has long been considered an important source of character information for taxonomic purposes and has been proposed as a feature that reflects the evolutionary history of plants [1]. Seed size, shape, and epidermal surface features have figured prominently in the characterization of seed morphological diversity [2,3], and it has been argued that these seed characters may provide data for circumscribing taxa at different taxonomic levels [1,2]. While some studies support this hypothesis [4,5], other investigations show that the systematic and taxonomic value of seed micromorphology may be limited [69]. The Melastomataceae are one of the largest flowering plant families [10], with 166179 genera and over 5,400 species mainly distributed in tropical and subtropical areas of the world [1113]. The vegetative and reproductive characters are very diverse across the family [10,14], and seed morphology is no exception. Seed morphological features have been used in the past for circumscribing a number of infrafamilial taxa [1518]. However, more recent investigations have found that seed morphological traits do not always correspond to proposed classifications [1922]. These studies suggested that the delimitation of some tribes and genera should be reconsidered using seed morphology based on the assumption that seed morphology yields information about the evolutionary history of the groups under study. The Miconieae, one of some 20 tribes in the Melastomataceae (Darin Penneys et al., unpublished data), comprises over 1,850 species and ca. 17 genera restricted to the New World [23]. Analyses of DNA sequence data have shown that all but one of the genera of Miconieae, as currently circumscribed, are not monophyletic [2326], supporting the notion that they are ambiguously defined and are frequently difficult to distinguish [18,2730]. Seed morphological features in the tribe are diverse and variable [31], but they do not support established classifications at generic and sectional levels [22,26]. However, some studies that incorporated a phylogenetic framework have identified a number of seed characters that are potential synapomorphies for certain clades [26,32], but taxon sampling remains insufficient for drawing definitive conclusions for the Miconieae as a who (...truncated)