306American Journal of Botany 98(2): 306–325. 2011.American Journal of Botany 98(2): 306–325, 2011; http://www.amjbot.org/ © 2011 Botanical Society of Americamorphologically heterogeneous and ecologically diverse. Growth forms include large tropical rainforest trees, temperate and high altitude tropical herbs and shrubs, and aquatic plants of swift-fl owing rivers and streams. Although their distribution is nearly cosmopolitan, their greatest species diversity is in the tropics. This well-supported clade contains fi ve families ( APG III, 2009 ; Wurdack and Davis, 2009 ) representing 94 genera and ~1900 species ( Kato, 2006 ; Cook and Rutishauser, 2007 ; Ste-vens, 2007a , b ; Weitzman et al., 2007 ; Thiv et al., 2009 ; Koi and Kato, 2010 ; Tippery et al., in press ): Bonnetiaceae, Calo-phyllaceae, Clusiaceae s.s., Hypericaceae, and Podostemaceae. The clusioids, excluding Podostemaceae, are an important component of tropical forests and comprise ~3% of the total species diversity in the Center for Tropical Forest Science ’ s global network of tropical forest research plots ( CTFS, 2009 ). Podostemaceae, the largest strictly aquatic fl owering plant family, play a key role in river systems — especially through their impact on the ecology and nutrition of fi sh and inverte-brates ( Allan, 1995 ; Machado-Allison et al., 2003 ). This fam-ily occupies a unique ecological niche for angiosperms: growing fi rmly attached to solid substrates in swift-fl owing, nutrient-poor rivers and waterfalls ( Philbrick and Novelo, 2004 ). Their ability to attach to substrates in these harsh environments is fa-cilitated by biofi lms partially composed of cyanobacteria, which may function as an important source of nitrogen for the plants The clusioids are a clade of fl owering plants in the large rosid order Malpighiales ( Savolainen et al., 2000 ; Soltis et al., 2000 ; Wurdack and Davis, 2009 ). Species in this clade are 1 Manuscript received 12 September 2010; revision accepted 13 December 2010. The authors thank the following individuals and herbaria for providing tissue or genomic DNA: M.C.E. Amaral, A. Amorim, P. Berry, D. Erickson, J.P. Ghogue, M. Kato, M. Kent, J. Kress, C. (Notis) Mella, D. Soltis, P. Soltis, P. Sweeney, E. Wood, A, AAU, CEPEC, FLAS, FTG, GH, HUH, INB, K, KLU, MICH, MO, NY, TI, TNS, UEC, UPS, WCSU, WIS, Z, and ZT. They also thank M. Beilstein, M. Clements, K. Gandhi, B. Hammel, S. Mathews, C. (Notis) Mella, P. Stevens, P. Sweeney, A. Vicentini, and W. Zhang for invaluable discussions regarding aspects of clusioid biology, taxonomy, data analyses, or for helpful comments on our manuscript. M. Bartlett, R. McFarland, and M. Latvis are gratefully acknowledged for assisting with the laboratory work. Funding for this research was provided by the National Science Foundation (NSF) DDEP grant OISE-0936076 to B.R.R. and C.C.D. and the NSF Assembling the Tree of Life grant DEB-0622764 to C.C.D. B.R.R. was also supported by the American Society of Plant Taxonomists; the Arnold Arboretum, the David Rockefeller Center for Latin American Studies, and the Department of Organismic and Evolutionary Biology at Harvard University; and the Garden Club of America. 8 Authors for correspondence: (e-mail: [email protected]; [email protected]) doi:10.3732/ajb.1000354 P HYLOGENY OF THE CLUSIOID CLADE (MALPIGHIALES): EVIDENCE FROM THE PLASTID AND MITOCHONDRIAL GENOMES 1 Brad R. Ruhfel 2,8 , Volker Bittrich 3 , Claudia P. Bove 4 , Mats H. G. Gustafsson 5 , C. Thomas Philbrick 6 , Rolf Rutishauser 7 , Zhenxiang Xi 2 , and Charles C. Davis 2,8 2 Department of Organismic and Evolutionary Biology, Harvard University Herbaria, 22 Divinity Avenue, Cambridge, Massachusetts 02138 USA; 3 Rua Dr. M á rio de Nucci, 500, Cidade Universit á ria 13083-290, Campinas, Brazil; 4 Departamento de Bot â nica, Museu Nacional, Universidade Federal do Rio de Janeiro, Quinta da Boa Vista, Rio de Janeiro 20940-040, Brazil; 5 Ecoinformatics and Biodiversity, Department of Biological Sciences, Aarhus University, Ole Worms All é , Building 1137, 8000 Å rhus C, Denmark; 6 Western Connecticut State University, Biological & Environmental Sciences, 181 White Street, Danbury, Connecticut 06810 USA; and 7 University of Zurich, Institute of Systematic Botany, Zollikerstrasse 107, CH-8008 Zurich, Switzerland • Premise of the study : The clusioid clade includes fi ve families (i.e., Bonnetiaceae, Calophyllaceae, Clusiaceae s.s., Hyperi-caceae, and Podostemaceae) represented by 94 genera and ~1900 species. Species in this clade form a conspicuous element of tropical forests worldwide and are important in horticulture, timber production, and pharmacology. We conducted a taxon-rich multigene phylogenetic analysis of the clusioids to clarify phylogenetic relationships in this clade. • Methods : We analyzed plastid ( matK , ndhF , and rbcL ) and mitochondrial ( matR ) nucleotide sequence data using parsimony, maximum likelihood, and Bayesian inference. Our combined data set included 194 species representing all major clusioid subclades, plus numerous species spanning the taxonomic, morphological, and biogeographic breadth of the clusioid clade. • Key results : Our results indicate that Tovomita (Clusiaceae s.s.), Harungana and Hypericum (Hypericaceae), and Ledermann-iella s.s. and Zeylanidium (Podostemaceae) are not monophyletic. In addition, we place four genera that have not been included in any previous molecular study: Ceratolacis , Diamantina , and Griffi thella (Podostemaceae), and Santomasia (Hypericaceae). Finally, our results indicate that Lianthus , Santomasia , Thornea , and Triadenum can be safely merged into Hypericum (Hypericaceae). • Conclusions : We present the fi rst well-resolved, taxon-rich phylogeny of the clusioid clade. Taxon sampling and resolution within the clade are greatly improved compared to previous studies and provide a strong basis for improving the classifi cation of the group. In addition, our phylogeny will form the foundation for our future work investigating the biogeography of tropical angiosperms that exhibit Gondwanan distributions. Key words: Garcinia mangostana ; Guttiferae; Hypericum perforatum ; mangosteen; matK ; matR ; morphology; ndhF ; rbcL ; St. John ’ s wort.307February 2011]Ruhfel et al. — Clusioid