A reappraisal of the turtle-orchids, genus Chelyorchis (Oncidiinae: Orchidaceae): Molecular, phylogenetic, and morphometric approaches1

Journal of the Torrey Botanical Society, Apr-Jun 2009 by Fern�ndez-Concha, Germ�n Carnevali, de Stefano, Rodrigo Duno, Romero-Gonz�lez, Gustavo A, Balam, Ricardo, Ix, William Cetzal, Tapia-Mu�oz, Jos� Luis, Ram�rez, Iv�n M

CARNEVALI FERN�NDEZ-CONCHA, G., AND R. DUNO DE STEFANO (Herbario CICY, Centro de Investigaci�n Cient�fica de Yucat�n, M�rida, Yucat�n 97200, Mexico), G. A. ROMERO-GONZ�LEZ (Orchid Herbarium of Oakes Ames, Harvard University Herbaria, Cambridge, MA 02138, USA), R. BALAM (Herbario CICY, Centro de Investigaci�n Cient�fica de Yucat�n, M�rida, Yucat�n 97200, Mexico), W. CETZAL IX (El Colegio de la Frontera Sur, Unidad Chetumal, Chetumal, Quintana Roo 77000, M�xico), J. L. TAPIA-MU�OZ AND I. M. RAM�REZ (Herbario CICY, Centro de Investigaci�n Cient�fica de Yucat�n, M�rida, Yucat�n 97200, Mexico). A reappraisal of the turtle-orchids, genus Chelyorchis (Oncidiinae: Orchidaceae): Molecular, phylogenetic, and morphometric approaches. J. Torrey Bot. Soc. 136: 164-185. 2009.-A review of live, herbarium, and bibliographic material of Chelyorchis revealed considerable floral variation that appears to be geographically correlated. We assessed whether the genus included one or more taxonomic entities using a morphometric analysis that involved the study of principal component analysis across several floral characters in 70 specimens, representing both geographical range and morphological variation. To further establish the phylogenetic relationships of Chelyorchis within the Cuitlauzina-clade, and to analyze the evolution of relevant characters, we performed a combined analysis using nrITS, morphological, and gapcoding data, which included only 13 species. Both of our phylogenetic analyses strongly support the genus Chelyorchis as a monophyletic entity that is sister to a clade comprised of the genera Ticoglossum and Rossioglossum. The morphometric evidence strongly suggests that two taxa at the level of species should be recognized, differing primarily in the shape and proportions of the labellum but also in their geographical distribution. A new species, Chelyorchis pardoi, is described and illustrated to accommodate the South American morph. Full description of the new species and iconography of both taxa are provided, and diagnostic features are discussed. The conservation status of the new taxon is assessed against IUCN criteria.

Key words: Chelyorchis ampliata, Chelyorchis pardoi, morphometrics, Neotropics, Oncidiinae, Oncidium ampliatum, Orchidaceae, phylogenetic analysis, IUCN Conservation Status.

John Lindley described Oncidium ampliatum in 1833 based on dry specimens collected by Hugh Cumming in Panama and western Colombia ("... in Panama, et Columbia Occidentali"; Lindley, 1833: 202; 1834). This orchid rapidly became one of the most popular species among horticulturists worldwide due to its ease of cultivation and because plants of this species bear large panicles of long lasting, showy, bright yellow flowers (Williams 1852, 1894, Hawkes 1965, Pridgeon 1992a, b).

Although the placement of this species in Oncidium Sw. was never challenged until recently, Oncidium ampliatum never fit neatly into any of the proposed infrageneric classifications. Both J. Lindley (1855) and Reichenbach f. (1861) placed it in section Pentapetala Macropetala because of its petals that are larger than the sepals. Closely following Kr�nzlin (1922), Garay and Stacy (1974) placed O. ampliatum in section Oblongata Kr�nzlin, sharing with other members of this assemblage (also polyphyletic because at least some of its species are referable to the genus Coppensid) the inconspicuous floral bracts, the subsimilar petals and sepals, free sepals that are much shorter than the labellum, and a callus composed of an odd number of tubercles. Recent phylogenetic analyses (e.g., Williams et. al. 2001a, Chase et al. 2005) indicated that this section is grossly polyphyletic since its former members fall within divergent clades in the Oncidiinae phylogenetic tree, and many of them are currently referred to different genera (e.g., Coppensia Dumort, Brevilongium E. A. Christenson, Psygmorchis Dodson & Dressier, and Oncidium Sw. sensu stricto).

Regardless of the sections to which it has been referred in the past, Oncidium ampliatum is aberrant in Oncidium by virtue of its thickly coriaceous, corrugate, convex pseudobulbs that are partially enveloped by sheaths lacking foliar blades, (as opposed to pseudobulbs enveloped by leaf-bearing sheaths), its thick, 2-3 coriaceous leaves (vs. the thinly coriaceous leaves present in most species of the genus), its petaloid, flabellate-fimbriate clinandrium, the flabellate-reniform wings (stelidia) of the column, and its short, broad, reniform tegula bearing two narrowly oblong pollinia (for pollinaria see Chase 1987: 14, Figs. 35-36). Furthermore, when in bud, the pedicel of the flower is always bent toward the apex of the inflorescence. Its preferences for dry forest are also unusual among true members of Oncidium. Also, orchid hybridizers have long known that Oncidium ampliatum was almost impossible to breed with other members of the genus Oncidium (this species, despite its horticultural popularity, hardly appears in intergeneric or infrageneric hybrid lists, e.g., Royal Horticultural Society 2008). Halbinger (1982), based on floral and vegetative similarities, suggested that O. ampliatum was related to Rossioglossum (Schltr.) Garay & G.C. Kenn., a member of the phenotypically and ecologically quite dissimilar Rhynchostele Rchb.f. complex from Mesoamerica. Chase and Palmer (1992), in a phylogenetic analysis of the Oncidiinae based on the plastid DNA restriction site variation of 51 species, established that O. ampliatum was not related to the "core" Oncidium assemblage, as typified by O. altissimum (Jacq.) Sw. (see Brummit 1978) but instead that it was in a clade placed near the base of the Oncidiinae phylogenetic tree that also included genera such as Ticoglossum Rodr. ex Halb., Rossioglossum, and Osmoglossum (Schltr.) Schltr., plus the "mule ear Oncidiums," Lophiaris Raf. and related taxa, including Trichocentrum Poepp. & Endl. Chase and Palmer (1992) called this assemblage the "Lophiaris clade."