Abstract
SummaryTwo decades have passed since DNA evidence first demonstrated an intimate relationship between the circumboreal species 'Coeloglossum' viride and the temperate Eurasian genus Dactylorhiza s.s. Most subsequent molecular phylogenies showed 'C.' viride to diverge after the D. incarnata group. The law of monophyly therefore dictated inclusion in Dactylorhiza of 'C.' viride, irrespective of its undeniably distinctive morphology. Those orchid enthusiasts still determinedly seeking reasons for retaining the genus Coeloglossum have often used as a justification the one published molecular study that suggested that D. viridis diverged earlier than D. incarnata. Interestingly, these respective phylogenetic positions are supported by recent data-rich studies based on next-generation sequencing. However, recent DNA phylogenies also show that D. iberica — long regarded as morphologically distinct but nonetheless universally accepted as belonging within the genus — diverged penecontemporaneously with D. viridis. Thus, in order to justify maintaining 'Coeloglossum' as a separate monotypic genus it would also be necessary to transfer D. iberica to a new monotypic genus, thus recognising two genera that are not only monotypic but also show only modest molecular divergence from the remaining dactylorchids. Examining in greater detail the morphology and micromorphology of D. viridis and D. iberica, we show that both species possess multiple morphological character states that are unique within the genus Dactylorhiza, but argue that greater phenotypic disparity is commonly the case in early-divergent lineages per se. Review of previous publications discussing D. iberica revealed little knowledge of its autecology, and contradictory DNA-based inferences that can be traced back to just two original specimens. We also suggest that morphological and molecular variation within both species has been under-estimated and under-explored.
Highlights
During the last two decades it has become de rigueur to circumscribe supraspecific taxa by applying the principle of monophyly to evolutionary matrices that consist of DNA sequences derived from specific 'candidate' genes
The oblong, parallel-sided labellum reaches 4.5 – 6 mm, ending in a small, tooth-like central lobe that is exceeded by the lateral lobes, coloured anything from uniform yellowishgreen through to purplish-brown paling toward the spur entrance; it cannot be confused with that of any other dactylorchid (Figs. 1A, 2A – C)
Nor can the spur itself, which is a near-globose downward-oriented sac 1.5 – 2 mm in diameter, contrasting with the larger cylindrical-conical spurs that characterise the remainder of the genus
Summary
During the last two decades it has become de rigueur to circumscribe supraspecific taxa by applying the principle of monophyly (groups of species consisting of all the descendant species of a hypothetical shared ancestor) to evolutionary matrices that consist of DNA sequences derived from specific 'candidate' genes. Controversy has rarely been greater than that surrounding monophyletic classifications of north-temperate orchids following publication of the initial genus-level circumscriptions by Pridgeon et al (1997) and Bateman et al (1997). Most authors preferred either to wholly reject the contribution of DNA studies to orchid classification on the grounds that they were in some way unintuitive or to accept only those portions of the DNA-based classification they found intuitively acceptable. Few of these authors have made serious attempts to explain their reasoning in either conceptual or practical terms. Chase (a decision reviewed scientifically by Bateman 2009 and nomenclaturally by Cribb & Chase 2001)
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