Where do all the Epipactis orchids come from?

Botanists use the orchid genus Epipactis as a model for speciation, but unravelling its family tree has been difficult.

If you see an Epipactis helleborine orchid, you might want to keep a close eye on it. It’s prone to evolving into new species. “It is notoriously difficult to identify with any confidence ancestor–descendant relationships…,” say Gábor Sramkó and colleagues, in their article on Epipactis evolution in Annals of Botany. “Nonetheless, it is highly probable that E. helleborine is the ancestor of at least ten recently derived species, the majority of them near-obligate autogams.”

Epipactis orchids
Flowers of 28 Epipactis taxa representing the morphological variation displayed by the studied genus. Image: Sramkó et al. 2019.

The autogams are plants that reproduce through autogamy. This is reproduction through self-pollenation, as opposed to allogamy where flowers swap pollen to fertilize. Working out how the various Epipactis species relate to each other has been difficult. Pulling apart the relationships could help illuminate evolutionary pathways.

“There exists interest well beyond the realm of orchid studies in resolving the general questions of (1) whether transitions from allogamy to autogamy can be iterative…; (2) whether autogams can speciate to form further autogams…; and (3) whether autogams might even undergo ‘reverse speciation’ to form novel allogams. Capturing such transitions in the midst of a genuine evolutionary diversification would be an additional bonus…” say the authors.

“[W]e do now possess conclusive evidence that section Epipactis constitutes a clade,” say the team, following genetic analysis, “that all of the speciation events within the section have occurred comparatively recently, that each such event is underpinned by a molecular branch considerably longer than those within the group and that several unequivocal species have emerged from within a single ancestral species, E. helleborine s.s

The authors conclude that E. helleborine is currently undergoing an evolutionary radiation. The way the plant reacts to genotypic, phenotypic and environmental factors is the source of variety in the offspring of E. helleborine. This ability to adapt drives the species into new forms in new locations.

Further reading

Sramkó, G., Paun, O., Brandrud, M. K., Laczkó, L., Molnár, A., & Bateman, R. M. (2019). Iterative allogamy–autogamy transitions drive actual and incipient speciation during the ongoing evolutionary radiation within the orchid genus Epipactis (Orchidaceae). Annals of Botany, 124(3), 481–497. https://doi.org/10.1093/aob/mcz103