Above and below: hybrids of Gymnadenia conopsea and Dactylorhiza fuchsii. Gymnadenia conopsea can hybridise with the Common Spotted Orchid (Dactylorhiza fuchsii) and more rarely with the Pyramidal Orchid
(Anacamptis pyramidalis) both of which also grew and flowered at this site when observations were made. These hybrids were instantly recognisable as dactylorhiza-like flowers but much smaller than usual, similar in size to the small flowers of Gymnadenia. Inspection of the labellum confirmed its intermediate shape. However, the spurs were not especially longer than in Dactylorhiza, as is sometimes reported for the hybrids. Nevertheless, there was no doubt at all of their hybridity.

Above Gymnadenia conopsea s.s. (s.s. = sensu stricto, in the strict sense) the Common or Chalk Fragrant Orchid in Kent, UK. Click images to enlarge. A large population growing on species-rich calcareous grassland  was observed. Until recently, the three separated species: Gymnadenia conopsea, Gymnadenia densiflora and Gymnadenia borealis were all classified as subspecies or variants of Gymnadenia conopsea s.l. (s.l. = sensu lato, in the loose sense). A team of us recently redetermined the NHM's (NHM = Natural history museum, London, UK) British and Irish collection of Gymnadenia to separate the specimens into the three separate species. G. conopsea is found on dry calcareous grassland. G. densiflora (Marsh Fragrant
Orchid) generally prefers fens and wet grassland with an abundance of calcium. G. borealis (Heath Fragrant Orchid) is more common in the north of Britain and often occurs on grassy moorland, which may be slightly acidic, and is more tolerant of a wider range of pH than the other two species.

As the name suggests, G. densiflora, tends to produce a spike of denser flowers, which is also often taller with more flowers, however, the ranges for the three species overlap and so this is not a reliable determinant. Morphologically, the lateral sepals and labellum (lower lip) also differ.

This is Gymnadenia conopsea var. albiflora, a not uncommon form lacking anthocyanin pigment. It is hypothesised that this variety is more attractive to nocturnal pollinators which can use their vision to locate white flowers in very dim light.

Gymnadenia flowers also produce scent (said to be sickly-sweet in G. conopsea, spicy-sweet in the other two species). It has been noted that the scent becomes stronger at dusk (Harrap and Harrap 2005, Orchids of Britain & Ireland: A field and site guide, 2nd ed. A & C Black, London) which might further attract nocturnal pollinators, however, studies generally show that diurnal pollinators are overall more important (discussed below).

The top of the labellum and the ends of the lateral sepals possess osmophores or scent-secreting cells (Spiczynska, 2001). These are conical epidermal cells (extending into short hairs or trichomes on the labellum margin) with numerous tiny pores in their cuticle. Invaginations of the cell membrane beneath the cuticle fill with secretory bodies which merge with the cuticle to release the scent through the cuticular pores. The labellum apparently has no stomata through which secretion could occur.

note the variable amount of deflexion of the lateral sepals, but overall is more suggestive of G. conopsea.

Above and below: different stages in development. Gymnadenia conopsea is pollinated by butterflies and diurnal and nocturnal moths. The flowers offer a nectar reward in their long spurs; pollination is efficient and fruit set is good.

Flower colour is generally pale pink or pale purple, but varies quite a bit in intensity.

In pressed and dried herbarium specimens the most reliable characteristics left to go on are the shape of the labellum and lateral sepals. Try to avoid using flowers at the very top of the spike as they often tend to look more borealis-like when not fully expanded, similarly the most mature flowers at the base may also look different as their labellums senesce (the flowers open at the base of the spike first and then anthesis progresses gradually towards the apex). Individual flowers can be quite variable on the same spike, so try to observe several and decide on a consensus morphology. It took a team of us to agree on more difficult specimens by consensus opinion. The three species are thought to freely hybridise and there are habitats where all three species are known to occur, for example calcaerous grassland with variable pH and moisture due to groundwater flows. Knowledge of the distributions of each of the three can also help verify determinations. It is impossible to achieve 100% accuracy, but analyses of the end results of our efforts strongly suggest that we got most of them right!

Above: a fairly typical specimen of G. conopsea. All the specimens photographed on this page are from two sites in Kent, UK: calcareous grassland rich in species. This area is well-known as a G. conopsea site, with no records of the other two species, however, there is still considerable variation as we shall show. Perhaps the single most reliable character is the overall shape of the labellum: square, long or broad.

Below: This plant has features of G. borealis with the weakly divided labellum, however, the lip is still squarish in contour and borealis is highly unlikely in this locale and I would still consider this to be G. conopsea.

These less densely-flowered individuals enable is to see the long
arc-shaped projecting spurs containing nectar at the back of the
flowers (each is a continuation of the base of the lip.

A study on Norwegian populations (Sletvold et al. 2012) showed that about 40 different Lepidoptera (moths and butterflies) acted as pollinators. The presence of both nocturnal and diurnal pollinators gave the highest fruit set, but of these daytime visitors made the greater contribution. These studies revealed that pollinators preferentially selected plants that were taller and more visible, had more flowers and had longer spurs. A longer spur means that the flower can contain more nectar for those pollinators with a proboscis long enough to reach it (spur length is proportional to nectar volume). Selection for high flower number was stronger with nocturnal pollinators, whilst longer spurs were more strongly selected for by nocturnal pollinators. The pollinia attach to the proboscis of the  pollinator and may be unable to reach the stigma on short-spured flowers which are thus selected against.

Above: fruit set. The more suitable pollen transferred to the stigma of
a flower, the larger the fruit produced since it contains more seeds. The fitness of an orchid such as this can be defined as the number of fruits multiplied by mean fruit mass.

Gymnadenia conopsea

The lateral sepals tend to be pointed at the tips and deflexed (angled downwards) about 30 degrees (sepal angle is largely lost as a trait in pressed herbarium specimens). The lip is more-or-less square in outline, and distinctly three-lobed with the central lobe usually the longest.

Gymnadenia densiflora

The lateral sepals are generally linear in shape and held out horizontally. The lip is generally broader than long and has
distinctive shoulders which sweep outwards in a more convex fashion than in G. conopsea.

Strong genetic differences have been shown between G. conopsea and G. densiflora (Stark et al. 2011) reinforcing their separation at the species level.

Gymnadenia borealis

The lateral sepals are more oval in contour and pointed at the tips. The lip is longer than broad and often indistinctly lobed, or with a prominent central lobe and small side-lobes,
more 'tongue-like' and the side lobes are often angular.