AOBPreview originally published online on January 9, 2009
Annals of Botany 2009 104(3):403-416; doi:10.1093/aob/mcn257
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This article appears in the following Annals of Botany issue: Special Issue: Orchid Biology [View the issue table of contents]
Phylogenetic relationships of Cranichidinae and Prescottiinae (Orchidaceae, Cranichideae) inferred from plastid and nuclear DNA sequences
1 Departamento de Botánica, Instituto de Biología, Universidad Nacional Autónoma de México, Apartado Postal 70-367, 04510 México, DF, Mexico
2 Departamento de Ciencias Biológicas, Universidad de los Andes, Apartado Aéreo 4976, Bogotá, DC, Colombia
3 Jodrell Laboratory, Royal Botanic Gardens, Kew, Richmond, Surrey TW9 3DS, UK
* For correspondence. E-mail g.salazar{at}ibiologia.unam.mx
Received: 2 June 2008 Returned for revision: 21 August 2008 Accepted: 13 November 2008 Published electronically: 9 January 2009
Background and Aims: Phylogenetic relationships of subtribes Cranichidinae and Prescottiinae, two diverse groups of neotropical terrestrial orchids, are not satisfactorily understood. A previous molecular phylogenetic study supported monophyly for Cranichidinae, but Prescottiinae consisted of two clades not sister to one another. However, that analysis included only 11 species and eight genera of these subtribes. Here, plastid and nuclear DNA sequences are analysed for an enlarged sample of genera and species of Cranichidinae and Prescottiinae with the aim of clarifying their relationships, evaluating the phylogenetic position of the monospecific genera Exalaria, Ocampoa and Pseudocranichis and examining the value of various structural traits as taxonomic markers.
Methods: Approx. 6000 bp of nucleotide sequences from nuclear ribosomal (ITS) and plastid DNA (rbcL, matK-trnK and trnL-trnF) were analysed with cladistic parsimony and Bayesian inference for 45 species/14 genera of Cranichidinae and Prescottiinae (plus suitable outgroups). The utility of flower orientation, thickenings of velamen cell walls, hamular viscidium and pseudolabellum to mark clades recovered by the molecular analysis was assessed by tracing these characters on the molecular trees.
Key Results: Spiranthinae, Cranichidinae, paraphyletic Prescottia (with Pseudocranichis embedded), and a group of mainly Andean ‘prescottioid’ genera (the ‘Stenoptera clade’) were strongly supported. Relationships among these clades were unresolved by parsimony but the Bayesian tree provided moderately strong support for the resolution (Spiranthinae–(Stenoptera clade-(Prescottia/Pseudocranichis–Cranichidinae))). Three of the four structural characters mark clades on the molecular trees, but the possession of a pseudolabellum is variable in the polyphyletic Ponthieva.
Conclusions: No evidence was found for monophyly of Prescottiinae and the reinstatement of Cranichidinae s.l. (including the genera of ‘Prescottiinae’) is favoured. Cranichidinae s.l. are diagnosed by non-resupinate flowers. Lack of support from parsimony for relationships among the major clades of core spiranthids is suggestive of a rapid morphological radiation or a slow rate of molecular evolution.
Key words: Cranichideae, Cranichidinae, matK-trnK, molecular phylogenetics, nrITS, Orchidaceae, Prescottiinae, resupination, trnL-trnF
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