Yet more beautiful monocots – some other UK orchids

Unless I get distracted by more orchids on Cyprus, this will be more of a photoblog of some of the other genera of orchids I’ve seen in the UK, many of which include just a single species, though Rose (The Wildflower Key) lumps some in with Orchis species and some with Dactylorhiza. For want of a better idea, I’m going to order these others as they are in Rose.

The first group are the helleborines, orchids with no basal rosette of leaves and flowers in long, dense spikes.  They have a different flower structure to some of the orchids I’ve looked at previously in that the lower lip (labellum) is divided into an inner (hypochile) and outer (epichile) part – the cup-shaped hypochile usually contains a nectar reward and the epichile provides a landing platform for insect pollinators. The same quarry sites locally where I’ve seen bee orchids host large populations of Dark-red helleborine, Epipactis atrorubens, the only helleborine I’ve seen in flower.  These are statuesque plants, even before the flowers open; up to 30 cm tall and with up to 20 drooping flowers on each spike.

Epipactis atrorubens at Bishop Middleham Quarry SSSI and Thrislington NNR

Some helleborines are self-pollinated but E. atrorubens is pollinated by wasps and other insects so has a projecting beak inside the flower which separates the anthers from the stigma to prevent self- pollination.

Common twayblade, which used to be called Listera ovata, is amongst the easiest of my local orchids to identify and also the most abundant.  Another tall orchid, its common name comes from the single pair of broad leaves, visible long before the flower spike emerges.  Its new scientific name, Neottia ovata, was given when molecular phylogenetic studies showed its genetic similarity to the very different looking Bird’s-nest orchid, Neottia nidus-avis. That raises some interesting questions – Bird’s-nest orchid is a parasitic plant, lacking chlorophyll and the ability to photosynthesise.  It obtains all the nutrition it needs from the roots of trees such as beech, in its woodland habitat. Because orchids produce very tiny seeds, nearly all rely on mycorrhizal fungal partners to establish themselves initially but Bird’s nest orchid seems to have taken the process one step further.

OLYMPUS DIGITAL CAMERA

Neottia ovata at Thrislington NNR

Common twayblade flowers are yellowy-green, with an open hood formed from the sepals and two side petals and a long labellum, divided in two for around half of its length – the first orchid flower I’ve described with a vaguely human appearance! It is mostly pollinated by wasps, sawflies and beetles and, along with the Bird’s-nest orchid, is unusual in that the pollinia are not attached to the outer surface of the rostellum but lie free on top of it.   The long labellum has a nectar-secreting furrow so, when a small insect lands on the broader end and crawls up, lapping up the nectar, it will eventually bump its head on the tip of the rostellum. This causes the rostellum to explode and the sticky liquid it ejects glues the pollinia firmly to the head of the unsuspecting insect, which will deposit the pollen on the next flower it visits.

1862_Orchids_F800_fig18

Common twayblade, Neottia ovata, from Darwin’s, ‘On the various contrivances by which British and foreign orchids are fertilised by insects, and on the good effects of intercrossing’ 
col. summit of column; a. anther; p. pollen; r. rostellum; s. stigma; l. labellum; n. nectar-secreting furrow.

A. Flower viewed laterally, with all sepals and petals, except the labellum, removed.
B. Ditto, with the pollinia removed, and the rostellum more reflexed after its explosion.

Darwin records seeing an ‘extremely minute Hymenopterous insect vainly struggling with its whole head buried in the hardened viscid matter, thus cemented to the crest of the rostellum and to the tips of the pollinia’ – the insect was smaller than one of the pollinia and was not strong enough to remove them after the explosion so it ended up glued permanently to the flower!

The next pair of orchids on my list are the Fragrant- and Marsh-fragrant orchids but this is where things start to get confusing.  Some authorities list three subspecies of Fragrant orchid (Gymnadenia conopsea agg.), whereas others call Marsh fragrant-orchid a separate species, G. densiflora.  I’m going to go with the latter, because I’ve chosen to use Rose as my reference.  I’ve not see the third species/subspecies, G. borealis, in any case.   What all the Fragrant orchids have in common, as you might expect, is very long, nectar-filled spurs on the flowers and a strong scent.

 

Left; Fragrant orchid, Gymnadenia conopsea, showing long spur (Bishop Middleham Quarry SSSI). Flowers spikes on right may be G. densiflora (Raisby Hill grassland)

Apart from the oversize spur, the flower structure of Fragrant orchids is quite like Orchis species and, similarly, hawk-moths are important pollinators.

My stand out orchid of 2017 was the beautiful Greater butterfly-orchid, Platanthera chlorantha, seen in a meadow near Ennerdale in the Lake District.  Its delicate green-tinged flowers and delicate scent mark it out as something special.

Greater butterfly-orchid, Platanthera chlorantha 2

Greater butterfly-orchid, Platanthera chlorantha 

Like Fragrant orchids, Butterfly orchids are pollinated by moths, particularly night-flying ones, and their long spurs produce the necessary nectar and scent.  The photo above shows the twisting of the ovary (resupination) which is a feature of nearly all orchids.  This occurs during flower development because the labellum or lip is actually derived from an upper petal but needs to be at the bottom of the flower to act as an insect landing pad.  The flowers of the Lesser butterfly orchid (P. bifolia) look very similar but have a less elongated labellum and the pollinia lie parallel to one another rather than being close at the top of the flower and more widely separated at its base.

It’s easy to see the twisted ovaries behind Frog orchid flowers too – when I first found these small, well-camouflaged plants in Thrislington NNR I thought they were some kind of helleborine because of the ‘helmet’ of sepals, but closer inspection showed the characteristic long labellum with a tiny tooth between two larger segments at the tip. The flowers are pollinated by bees and small wasps, though they can also self-pollinate.

Frog orchid, Coeloglossum viride (or Dactylorhiza viridis) Thirslington NNR

Frog orchids prefer ancient chalk grassland and meadows so its good to see them thriving at Thrislington on a small area of thin, lime-rich soil next to the working quarry.  Just as the Twayblades have been reclassified on molecular genetic evidence, C. viride is now often placed with the Marsh- and-Spotted orchids, with which it sometimes hybridises, as Dactylorhiza viridis.

I think that takes my tally of UK orchids seen to 13, so I still have a long way to go – I’m sure I’m not the only person to have been inspired by Leif Bersweden and Jon Dunn recently.  Perhaps the most remarkable thing I’ve learned in this brief survey of UK orchids, and how they are pollinated, is what an amazing observational scientist Charles Darwin was.  I thoroughly recommend his book, ‘On the various contrivances by which British and foreign orchids are fertilised by insects, and on the good effects of intercrossing’, available in full via the Darwin online project.   Darwin describes the flower structures in exquisite detail and spent hours watching the pollination process and conducting simple experiments to confirm the function of each part.  The ultimate ‘timewaster’ – look where it got him!

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