Systematics and conservation of British and Irish orchids: a "state of the union" assessment to accompany Atlas 2020.

Summary: Prompted by concurrent completion of the latest plant atlas for Britain and Ireland, the orchid flora of these islands is reviewed in detail, focusing on 21st century progress in both systematics research and formal conservation categorisation under IUCN criteria. DNA-based phylogenies consistently circumscribe monophyletic groups that constitute obvious genera, though relationships among those genera remain less certain and resistance to phylogenetic classification persists. Comparison of species circumscription studies in critical groups such as Dactylorhiza, Gymnadenia, Platanthera, Epipactis and Orchis shows that most of the recent progress has been achieved using DNA-based techniques, which have also greatly increased understanding of associated mycorrhizae. Most morphological studies remain disappointingly traditional, squandering opportunities for morphometric studies that identify discontinuities between species, allow comparison of rates of morphological and molecular evolution, and underpin accurate quantitative descriptions designed to aid identification. Possibly only one of the 53 species recognised as native is still viewed as endemic. Conventional views on the significance of both pollinator specificity and quantitative seed output as the preferred measure of fitness are questioned, and mycorrhizae are explored as possibly under-rated ecological filters. Comparison of species distributions in successive Atlases suggests diverse patterns of change that reflect a combination of habitat modification, climate change and, in a few cases, improved identification skills. Ecologically tolerant lowland species such as Ophrys apifera and Dactylorhiza praetermissa are migrating northward rapidly, while the genus Serapias appears to be mounting a cross-Channel invasion. Most formal Red-Listing categorisations, and the underlying IUCN criteria, are supported for decisions made within the British Isles, but unfortunately, they have translated poorly into the equivalent European and Global lists. Within Britain, the Data Deficient category has been employed too frequently and illogically; ironically, it is sometimes used to penalise species for having been the subjects of serious research. Far from being "complete", the present consensus view on the taxonomy and evolution of the glacially impoverished British and Irish flora is judged both parochial and complacent. Reinvigorated UK-based research programmes that integrate quantitative morphological and molecular studies of British and Irish natives in a European context are urgently needed. [ABSTRACT FROM AUTHOR]