Implications of next-generation sequencing for the systematics and evolution of the terrestrial orchid genus Epipactis, with particular reference to the British Isles

Abstract

SummaryRecent application of next-generation sequencing technology to Eurasian taxa of the primitive epidendroid orchid clade Epipactis section Epipactis has further advanced our knowledge of what has become a model system for studying the origins of numerous autogamous taxa from within arguably only one allogamous ancestral species, E. helleborine s.s. Current understanding of evolutionary pattern, species re-circumscription and speciation process within Epipactis is critically reviewed, emphasising the relevance of recent research based on next-generation sequencing and aiming to better understand taxa native to the British Isles. Conclusions include recognition that (1) the majority of named taxa currently widely viewed as species do not pass rigorous tests of species status, (2) two of the six unequivocal species native to Britain extend further east in Eurasia than was previously supposed, and none is endemic, (3) all scientifically defensible species of Epipactis have high frequencies of self-pollination (although autogamy is significantly less frequent in the ancestral species E. helleborine than in any of the remaining species derived from it), and (4) fully understanding the speciation process (including substantial increases in autogamy) will require us to further investigate not only pollinator behaviour and the diverse factors determining gynostemium morphology but also the equally diverse factors (including mycorrhizal specificity) likely to influence the invasion of novel, challenging habitat types.