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Evolution of Europe’s rarest orchid

Kew researchers study the evolution of arguably Europe’s rarest orchid on the Azores.

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Photo of Platanthera azorica

Platanthera azorica, recently recognised as the rarest of the three butterfly-orchids on the Azores (Photo: R. Bateman)

The IUCN Red List of endangered species currently recognises only one species of butterfly-orchid on the mid-Atlantic Azorean archipelago. However, a recent monographic study, published in PeerJ, unequivocally revealed the presence of three butterfly-orchid species on the islands, although it reinforced the idea of a single immigration event by airborne seed from mainland Europe. Of the two less frequent species, one is an exceptionally good indicator of remaining areas of semi-natural laurisilva vegetation and the other is arguably Europe’s rarest orchid.

In a further study, just published in the American Journal of Botany, morphometric measurements and DNA-based analyses of both the orchids and their mycorrhizal partners revealed that the species could not only be differentiated using morphology but, more remarkably, by their mycorrhizal partners. The most widespread of the three orchids forms partnerships with several fungi, whereas the far more specialised requirements of the two rarer species may have played a role in their speciation. Substantial changes in the relative and absolute sizes of flower parts are also evolutionarily significant.

The study revealed cases of speciation with (cladogenesis) and without (anagenesis) lineage splitting, demonstrating that these orchids constitute an excellent model system for investigating plant diversification on islands.

References

Bateman, R. M., Rudall, P. J. and Moura, M. (2013). Systematic revision of Platanthera in the Azorean archipelago: not one but three species, including arguably Europe’s rarest orchid. PeerJ1: e218 Available online

Bateman, R. M., Rudall, P. J., Bidartondo, M. I., Cozzolino, S., Tranchida-Lombardo, V., Carine, M. A. and Moura, M. (2014). Speciation via floral heterochrony and presumed mycorrhizal host switching of endemic butterfly orchids on the Azorean archipelago. American Journal of Botany 101: 979-1001. Available online

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