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Clarified relationship between Dactylorhiza viridis and Dactylorhiza iberica renders obsolete the former genus Coeloglossum (Orchidaceae: Orchidinae)

Bateman, RichardM., Rudall, PaulaJ.
Kew bulletin 2018 v.73 no.1 pp. 4
DNA, Dactylorhiza viridis, high-throughput nucleotide sequencing, microstructure, monophyly, phenotype, plant taxonomy, population ecology
Two 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.