Phylogenetics of Maxillariinae (Orchidaceae)

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This study is a continuation of our work on other subtribes of the tribe Maxillarieae, especially subtribes Oncidiinae, Stanhopeinae, and Zygopetalinae and is related to a new project on the subtribe Pleurothallidinae.


In recent years, orchid systematists have made great progress in clarifying evolutionary relationships among orchid genera, based largely upon cladistic analyses of both molecular and morphological/anatomical data sets. A well-supported outline of tribal and subtribal relationships is quickly emerging, limited primarily by the rate that rare taxa can be collected and analyzed. As such broad scale studies progress, it is becoming clear that one of the most daunting remaining tasks will be the phylogenetic revision of very large, species rich genera (e.g., Bulbophyllum, Epidendrum, Maxillaria, Pleurothallis). An even greater problem is that few taxonomists have the years of intensive study and breadth of knowledge to work with these large taxa. For example, few taxonomists are able to accurately identify a randomly-chosen Pleurothallis or Maxillaria species. Existing keys and subgeneric classifications are incomplete and are based upon admittedly artificial classifications.

To attempt a modern molecular and morphology-based phylogenetic revision of these huge genera, a broad collaboration is required among alpha-taxonomists who have intensive, detailed knowledge of the species, their variation and nomenclature, and molecular systematists who can generate and analyze the large data sets necessary to resolve these genera. We have assembled such a collaborative group, which includes: 1) herbarium/field botanists with years of study and deep knowledge of these species and their nomenclature; 2) orchid molecular systematists with experience in collecting and analyzing large combined DNA data sets; 3) pollination biologists; and 4) natural product chemists experienced in analyzing floral rewards.

Why study Maxillaria? This tribe (Maxillarieae) contains >2800 species (about 10% of Orchidaceae) and is a major component of the neotropical flora and epiphytic vegetation. The subtribe Maxillariinae (sensu Whitten et al. 2000) includes ±600-700 species currently divided into eight genera. Maxillaria ranks fourth in species-richness among genera of neotropical Orchidaceae but is still poorly known. Dressler (1993) estimated that approximately 420 species are accepted as valid species. Index Kewensis lists 634 names in the genus of which about 80 are perhaps synonyms for a probable mininum of 564 accepted species (Atwood, pers. comm.). Based on studies of Maxillaria from Costa Rica (Atwood and Mora de Retana, 1999), we believe that species numbers will exceed 620. These plants are often large, conspicuous, and numerically important components of the epiphytic vegetation in the Neotropics.

Generic limits have been chaotic for more than a century and current/ongoing taxonomic treatments offer little hope of stability unless the revisions are based upon well-sampled molecular/morphological cladograms. Preliminary molecular data (below) confirm the long-suspected paraphyly of Maxillaria s.l. Neotropical orchid floras must confront such taxonomically difficult genera in their treatments, but such treatments are hampered by conflicting, arbitrary, and unsupported non-monophyletic generic concepts proposed by various taxonomists. Our previous work has demonstrated that combined molecular data sets can yield highly supported cladograms that can serve as the basis for stable, objective classifications within this tribe (Whitten et al. 2000; Ryan et al. 2000; Williams et al. 2001a,b; Koehler et al. 2002).

This site contains: 1) molecular data matrices for Maxillarieae as self-extracting files, 2) cladograms from both published and unpublished studies in several subtribes, 3) literature references, 4) photographs, 5) biographical sketches of a number of collaborators, 6) a list of all known species of Maxillaria following the classification proposed by Atwood, Carnevali, and Dodson, and 7) links to some useful sites.

Acknowledgments - Kent Perkins helped tremendously in setting up this site, which I modified from the excellent Melastomataceae site of Darin Penneys and is used with his permission, for which I thank him greatly. Eric Christenson has been most helpful in pointing out extremely serious omissions in the literature that was published after this site was initially developed in December 2001. His kind, constructive suggestions are greatly appreciated. We are, of course, responsible for any additional errors and/or omissions and solicit polite, constructive criticisms. Funding was provided by U.S. National Science Foundation grant No. DEB-0234064 to N. H. Williams and W. M. Whitten for the project Systematics of Maxillariinae (Orchidaceae): Generic delimitation, pollinator rewards, and pollination. Additional funding was provided by a Furniss Foundation graduate student fellowship from the American Orchid Society to M. A. Blanco and by Kew Latin American Research Fellowships to M. A. Blanco (to study specimens in European herbaria) and to S. Koehler (to study systematics of the Maxillaria madida alliance). Funding was provided to R. Singer by a FAPESP postdoctoral grant 01/08958-1 and to G. Carnevali from CICY for the project "Orchidaceae Neotropicales".

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