Species limits and diversification in the Madagascar olive (Noronhia, Oleaceae) CYNTHIA HONG-WA 1,2 * and GUILLAUME BESNARD 3 1 Department of Biology, University of Missouri–St. Louis, One University Blvd, St. Louis, MO 63121-4400, USA 2 Missouri Botanical Garden, PO Box 299, St. Louis, MO 63166-0299, USA 3 CNRS, ENFA, Université Paul Sabatier, Laboratoire Evolution et Diversité Biologique, UMR 5174, 31062 Toulouse 4, France Received 10 December 2012; revised 2 July 2013; accepted for publication 17 August 2013 Studies of ecological and phenotypic diversity in adaptive radiations have greatly contributed to our understanding of the patterns and processes of species diversification, whilst also challenging our assessment of the nature of species. Here, analyses of bioclimatic, molecular and morphological data, interpreted in phylogenetic and geo- graphical contexts, were carried out to understand species limits in the Madagascar olive (Noronhia, Oleaceae). Most species hypotheses exhibit clear boundaries and are supported by at least one line of evidence, but a contrasting pattern of high morphological and ecological variation with relatively low nucleotide sequence divergence characterizes the diversification of Noronhia. This diversification was probably driven by fine-scale ecological and evolutionary processes, as suggested by the poor fit with four models of species diversification of the biota of Madagascar and the apparent lack of differentiation detected from large-scale bioclimatic data. Overall, this study offers useful insights into the patterns of plant diversification in Madagascar, the understanding of which requires good circumscription of species, improved knowledge of their distribution and operational models of diversification that take into account the particular biology of plants. © 2013 The Linnean Society of London, Botanical Journal of the Linnean Society, 2014, 174, 141–161. ADDITIONAL KEYWORDS: adaptive radiations – bioclimatic data – morphology – multivariate analyses – phylogeny – plant diversification. INTRODUCTION The unique and diverse biota of Madagascar testifies to adaptive radiations of a variety of groups of animals and plants (Goodman & Benstead, 2003; Vences, 2005). The island has been isolated from major landmasses since about 90 Mya (de Wit, 2003). Although some of the biota are assumed to be Gond- wanan relicts, most are thought to be derived from Tertiary African and Asian colonizers (Yoder & Nowak, 2006; Russell, Goodman & Cox, 2008; Warren et al., 2010; Kuntner & Agnarsson, 2011; Reddy et al., 2012; Buerki et al., 2013; Hong-Wa & Besnard, 2013). In particular, a good proportion of the Malagasy endemic plant genera originated in the Miocene onwards and show strong affinities, in decreasing order, with African, South-East Asian and Indian plant taxa (Buerki et al., 2013). Levels of taxonomic endemism and species diversity are high (Goodman & Benstead, 2003), endemism being estimated to be > 90% for non-volant and non-marine vertebrates and > 80% for vascular plants (Goodman & Benstead, 2003; Callmander et al., 2011). The spatial pattern of endemism is even more impressive, with many species having narrow ranges and being known from only one or a few localities (Schatz et al., 2000; Goodman & Benstead, 2003; Vences et al., 2009; Hong-Wa & Arroyo, 2012; Besnard et al., 2013). The plant genus Noronhia Stadman ex Thouars (Oleaceae), recently extended to include Afro- Malagasy relatives formerly placed in Chionanthus L. to accommodate phylogenetic relationships (Hong-Wa *Corresponding author. E-mail: cynthia.hong-wa@mobot.org Botanical Journal of the Linnean Society, 2014, 174, 141–161. With 3 figures © 2013 The Linnean Society of London, Botanical Journal of the Linnean Society, 2014, 174, 141–161 141