Volume 20, Issue 13 p. 2771-2786

An integrative approach to delimiting species in a rare but widespread mycoheterotrophic orchid

CRAIG F. BARRETT

CRAIG F. BARRETT

L. H. Bailey Hortorium and Department of Plant Biology, 412 Mann Library, Cornell University, Ithaca, NY 14850, USA

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JOHN V. FREUDENSTEIN

JOHN V. FREUDENSTEIN

Department of Evolution, Ecology, and Organismal Biology, The Ohio State University Museum of Biological Diversity, 1315 Kinnear Road, Columbus, OH 43212, USA

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First published: 13 May 2011
Citations: 69
Craig F. Barrett, Fax: (607) 255-5407; E-mail: [email protected]

Abstract

In the spirit of recent calls for species delimitation studies to become more pluralistic, incorporating multiple sources of evidence, we adopted an integrative, phylogeographic approach to delimiting species and evolutionarily significant units (ESUs) in the Corallorhiza striata species complex. This rare, North American, mycoheterotrophic orchid has been a taxonomic challenge regarding species boundaries, displaying complex patterns of variation and reduced vegetative morphology. We employed plastid DNA, nuclear DNA and morphometrics, treating the C. striata complex as a case study for integrative species delimitation. We found evidence for the differentiation of the endangered Cbentleyi (eastern USA) + Cstriata var. involuta (Mexico) from the remaining Cstriata (= Cstriata s.s.; USA, Canada, Mexico). Corallorhiza striata involuta and C. bentleyi, disjunct by thousands of kilometres (Mexico-Appalachia), were genetically identical but morphologically distinct. Evidence suggests the Cstriata complex represents three species: Cbentleyi, Cinvoluta and a widespread Cstriata s.s under operational criteria of diagnosability and common allele pools. In contrast, Bayesian coalescent estimation delimited four species, but more informative loci and a resultant species tree will be needed to place higher confidence in future analyses. Three distinct groupings were identified within Cstriata s.s., corresponding to Cstriata striata, Cstriata vreelandii, and Californian accessions, but these were not delimited as species because of occupying a common allele pool. Each comprises an ESU, warranting conservation considerations. This study represents perhaps the most geographically comprehensive example of integrative species delimitation for any orchid and any mycoheterotroph.

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