Biological Flora of the British Isles: Gymnadenia conopsea s.l.

This account presents information on all aspects of the biology of Gymnadenia conopsea (L.) R. Brown s.l. (Fragrant Orchid) that are relevant to understanding its ecological characteristics and behaviour. The main topics are presented within the framework of the Biological Flora of the British Isles: distribution, habitat, communities, responses to biotic factors, responses to environment, structure and physiology, phenology, floral and seed characteristics, herbivores and disease, history and conservation. Most available information was published before recent revisions in taxonomy split what had been known as Gymnadenia conopsea into three separate species, now designated G. borealis (Druce) R.M. Bateman, Pridgeon & M.W. Chase, G. conopsea (L.) R. Brown and G. densiflora (Wahlenb.) Dietrich. Although the three newly accepted species have at least partial reproductive isolation, they have numerous morphological and ecological similarities. Some recent work still refers to G. conopsea s.l. because of difficulties in distinguishing between the species, and inertia in adoption of the new taxonomy. Wherever possible, differences between G. borealis, G. conopsea s.s. and G. densiflora are highlighted. Gymnadenia conopsea s.l. is a perennial, terrestrial orchid that is widely distributed across Eurasia. The three segregate species are all considered native. G. conopsea s.s. (Chalk Fragrant Orchid) occurs mainly in the southern half of Britain, where it is most commonly observed in dry calcareous grasslands and pastures. G. densiflora (Marsh Fragrant Orchid) occurs in damp calcareous marshes, fens and dune slacks in England and Wales; it is rare in Scotland but frequent in Ireland. G. borealis (Heath Fragrant Orchid) is mainly found on hill pastures in Wales, northern England and Scotland. The three species all avoid shade, being most abundant in open habitats. Although the three segregate species cannot always be reliably distinguished on the basis of morphological characteristics, diagnostic features include plant height, leaf width and disposition, density of flowers in the inflorescence, shape of the labellum, spur width, and odour and colour of the flowers. Additionally, several cytotypes within G. conopsea s.s. have been observed in Central Europe. These often grow in mixed-ploidy populations; in contrast, the species appears to be predominantly diploid in Britain. Gymnadenia conopsea s.l. is a non-bulbous geophyte. Leaves emerge in spring, and flowering takes place between the end of June and the beginning of August. Vegetative adult dormancy the failure of above-ground parts to appear in a growing season, followed by reappearance of full-sized photosynthetic plants in subsequent years has been observed. Such dormancy rarely lasts longer than 1 year. The flowers of G. conopsea s.l. are arranged in a spike. The species is self-compatible but dependent on pollinators for successful pollination and fruit set. The most frequent pollinators are diurnal and nocturnal Lepidoptera. Pollinators are rewarded with abundant nectar produced within the long floral spur. In many populations, fruit set is > 90%. Although G. conopsea s.l. is widely distributed and can be locally abundant, the number of populations and size of populations in Britain have declined markedly during recent decades, mostly due to habitat destruction, ploughing of old fields and drainage. Because the distribution of the segregate species has been poorly documented, their conservation status is not well known. Conservation of remaining populations and restoration of degraded populations require reinstatement of appropriate management regimes (late summer/autumn mowing or grazing), combined with more detailed inventories of the three species.