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(American Journal of Botany. 2009;96:686-706.) doi: 10.3732/ajb.0800235 © 2009 Botanical Society of America, Inc.

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Phylogeny and classification of the species-rich pantropical showy genus Ixora (Rubiaceae-Ixoreae) with indications of geographical monophyletic units and hybrids¹

² UMS 2700 CNRS—USM 0602 MNHN: Taxonomie et Collections, Département de Systématique et Évolution, Muséum national d’Histoire naturelle, 16 rue Buffon 75005 Paris, France ³ Bergius Foundation, the Royal Swedish Academy of Sciences and Botany Department, Stockholm University, SE-106 91 Stockholm, Sweden

ABSTRACT

Species-rich genera often have various conflicting circumscriptions from independent regional flora treatments. Testing the monophyly of these groups of plants is an important step toward the establishment of a phylogenetic classification. The genus Ixora of the tribe Ixoreae in the subfamily Ixoroideae (coffee family or Rubiaceae) is a species-rich pantropical genus of ca. 500 species. Phylogenetic analyses of Ixoreae based on combined sequence data from one nuclear (nrETS) and two chloroplast (rps16 and trnT-F) markers reveal the paraphyly of Ixora as presently delimited and also show that the tribe can be subdivided into three major clades: the Mascarene/neotropical/Malagasy/African clade, the Pacific clade, and the Asian clade. Given the lack of morphological synapomorphies supporting the different Ixora clades and the morphological consistency of the ingroup taxa, we propose a broad circumscription of Ixora including all its satellite genera: Captaincookia, Doricera, Hitoa, Myonima, Sideroxyloides, Thouarsiora, and Versteegia. The current infrageneric classification of Ixora is not supported. The different Ixora subclades represent geographical units. Nuclear and chloroplast tree topologies were partially incongruent, indicating at least four potential natural hybridization events. Other conflicting positions for the cultivated species are most likely due to anthropogenic hybridization.

Key Words: hybridization • Ixora • molecular phylogenetics • nrETS • ornamentals • rps16 • Rubiaceae • taxonomy • trnT-F

Received for publication 10 July 2008. Accepted for publication 5 December 2008.

FOOTNOTES

¹ The authors thank Dr. P. De Block, F. Jacq, Dr. J.-F. Butaud, Dr. J.-Y. Meyer, and Dr. J. Munzinger for providing Ixora material for biomolecular studies; two anonymous reviewers for comments on the manuscript; the authorities of the North and South provinces of New Caledonia and the French Polynesian Government for access to the field and authorization to collect specimens and the tribal authorities who allowed us to work on their territories; the institutions of BR, G, K, L, MO, NOU, P, S, TAN, TEF, and UPS for granting access to herbarium collections and providing material for bio-molecular studies. Financial support was provided by the UMS CNRS 2700 – USM MNHN 0602 "Taxonomie et Collections", the Department "Systématique et Evolution", MNHN, Paris; the Missouri Botanical Garden through Dr. G. McPherson for support of fieldwork in New Caledonia; the European Commission’s Research Infrastructure Action via the SYNTHESYS Project (EU) to A.M. to access BR and L; the Swedish Research Council and the Knut and Alice Wallenberg Foundation to B.B.

⁴ Author for correspondence (e-mail: arnaud{at}bergianska.se)

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