Monitoring Butterfly Orchids in the Chilterns - 2018 Summary

During October I have been trying to catch up on analysing data and other information I collected on a few orchid projects during the summer.  

One of the more interesting has been the study of a population of Greater Butterfly orchids, made more enjoyable because the landowner is a keen and enthusiastic participant. 

I have now finished interpreting this year's data, and while the population is one of the biggest, if not the biggest in Oxfordshire, it is in quite a confined area of woodland in the Chilterns, shaded by beech and ash.  All the plants above ground in one half of this orchid patch have numbered markers so we can look at their fate year by year.

Here are a  a few highlights from this year (and some photos from the count of flowering plants in June):

There were around 500 plants in 2018 which produced 196 flowering spikes in an area of around 500 m2. The number of plants increased by at least 40% on last year, and the number of flowering spikes by 58%. This year's flowering plants were taller, had larger leaves than those last year, and the fruit set was higher. We are looking at climate influences.

Around 5% of the plants there last year did not appear this year, maybe dead or just dormant. 44% of the plants that flowered in 2017 did so again this year; they were more robust than those that did not repeat flower.

The population was made up by flowering plants (26%), what I term maturing plants with two leaves (26%) and juvenile plants with 1 leaf (48%). The pictures are of the same plant in full flower (June 6), showing the first leaves (April 10), in bud (May 8) and in fruit (Aug 10). Seed dispersal began end August.

Fruit set was more likely for flowers in the middle of the inflorescence rather than the top or bottom.

Much more detail is available in a progress report which can be accessed by following this Dropbox link:

2018 Progress Report A Study of a Population of Greater Butterfly Orchids in the Chilterns

Identification of orchids in fruit

Orchids flower in most cases for only 2 to 3 weeks, and most of them can be identified with certainty, though some experience is required for three genera, the fragrant orchids, the marsh orchids and the helleborines.   Hybrids are a further complication.  

Before flowering reliance on the leaf shape and arrangement can work; Poland and Clement's 'Vegetative Guide to the British Flora' is the best guide and Sean Cole and Mike Waller are working on a photographic guide to be published next year.   But post flowering, what then?  

Over the last few years, but particularly 2017 and 2018, I have been trying to develop a key for orchids in fruit, at a point where they have seed pods with viable seeds, and for most species leaves have withered away.   I have examined 30 species (out of a possible 54) and a further species where I only had a seed pods.  Of the remaining 23 species, 9 are protected and it is illegal to remove any part.  In any case they are pretty much site specific anyway as are another 5.  One has not been seen for years, 3 because of their diminutive size will be impossible to locate in fruit, so that I am left with 5 to look for in 2019, and one more needs further data.

I have measured from photos and direct measurement the angle of the fruits to the stem, the length and width of seed pods.   Using a microscope (x40 and x100) I have measured the length and width of seeds (actually the outer casing, the testa, provided that it contains an embryo.   Habitat, and extant leaves are also useful.  

Seed pod measures

Angle to stem

Seed measures

It does seem possible to discriminate, especially where for example the length / width ratio of seed pods is used rather than absolutes, and provided a reasonably large random sample has been used to determine parameters (5 seems to be enough).  

These are a couple of examples of filtering the results.

I am planning to have a poster on this at the upcoming BSBI meeting in November at Edge Hill.

Distinguishing Between Fragrant Orchids

Morphology does not seem to have caught up with molecular methods to discriminate between the 3 species of fragrant orchids in the UK: Marsh fragrant (Gymnadenia densiflora), Heath fragrant (G. borealis), Chalk fragrant (G. conopsea).   Their common names indicate their usual habitat preferences, and this is often the determinant when a fragrant orchid is recorded, but it is a bit unsatisfactory.

Last Saturday I visited Waitby Greenriggs, a Cumbria Wildlife Trust reserve where all three species are said to occur..   Its an old railway cutting with a ditch at the bottom, with Marsh helleborines in most areas, including part way up the embankments.  

 

Fragrant orchids were everywhere.  New Flora of the British Isles (3rd edn) - Stace,  gives a number of parameters to distinguish between them:

		Sepals	Lab W mm	Lab L mm	Sepal W mm	Sepal L mm	Spur mm	Lab W/L
	Gc	Point Down	5.5 to 6.5	5 to 6	1	5 to 6	12 to 14	1.1
	Gd	Horiz	6.5 to 7	3.5 to 4	1	6 to 7	14 to 16	1.8
	Gb	Point Down	3.5 to 4	4 to 4.5	2	4 to 5	11 to 14	0.9

Frankly there do not seem to be any other keys so this is a s good as it gets..

At Waitby I measured 16 plants, chosen pretty much at random as i walked across the reserve, though inevitably most were in the damper areas near the helleborines, though a few were on a dry bank.  I measured the all the above parameters, but in addition I measured the width and depth of the central lobe (in heath fragrant the labellum is obscurely lobed), and whether there were stomata on the upper surface of the leaf (Poland and Clements suggest that only Chalk fragrant has stomata).

I then tried to sort them out, firstly by making an assessment by eye, but  then using the measured parameters, I made a few adjustments to my initial conclusion.   A fellow orchid enthusiast also assessed some by eye from a Facebook posting (we agreed on most but differed on a couple.   What did seem to discriminate was the number of flowers on the spike (which I did not correct for height), and whilst the labellum width to length ratio was useful the separation was not as great as suggested in the literature:

	Flowers	Lab          W/L	Sepal         L/W	N
Marsh	29	1.47	2.7	8
Chalk	19	1.36	3.4	7
Heath	16	1.00	2.3	1

Nevertheless, these three measures taken together with a ot of weight on the flower density, and the presence or absence of stomata on the upper surface of the leaf should provide sufficient to properly attribute a plant to one of the three species.  

I added the number of flowers in as an afterthought, having attributed plants on all the other measures, but it looks like the most reliable single measure, particularly if corrected for height, so G. densiflora does seem very appropriate.

Chalk Fragrant

Marsh Fragrant

Heath Fragrant

Of course a big underlying assumption is that I correctly identified the plants in the first place and that Waitby greenriggs does indeed have all three species.  Sadly  I did not have my portable DNA tool with me on this occasion to confirm my results.

Butterfly Orchid Hybrids in Gloucestershire

I have been intrigued by the hybrid between Lesser and Greater butterfly orchids for 2 or 3 years now.  It is not common, not least because there are few places where the two parents grow together.  Our croft on Skye had both and there were a few hybrids, around 2 to 3 per year out of a total population of over 100.

Near Cranham and south towards Slad in Gloucestershire there seems to be a hotspot.   I have seen  are at Sheepscombe, Bulls Cross, and on Cranham Common.   On Sunday I went to another location in that general area, Butterfly Conservation's Strawberry Bank reserve. 
     

Strawberry Bank

On the bank itself there were mainly Lesser butterfly, while at the bottom near the woodland edge were a few Greater.  There were though amongst the Lesser a few hybrids, looking like the former but with the pollinia not parallel, yet not as wide as for Greater. 

Lesser

Greater

Hybrid

 I made a few measurements comparing one hybrid plant, one Greater and 7 Lesser:

	Subtended	Spur	Viscidia
	Angle deg.	Length mm	Distance mm
LBO (Av)	1.9	21.8	1.2
Hybrid	26.0	21.9	3.7
GBO	36.0	29.6	3.8

Note that the viscidia are the sticky pads at the bottom of the pollinia stem (caudicle). These are what attach the pollina to visiting insects to effect pollination.  

On this particular example the subtended angle was larger than others I found there.

Looking for hybrids I had less success when trying to find them again in 2 locations where the BSBI database has records.  At Bix, in BBOWT's Warburg reserve, Greater are scattered throughout, though never plentiful.  There are just a few Lesser, actually growing close to Greater, but there were no hybrids.  Probably not enough of both parents.

Llynclys Common in Shropshire is another site where there is a record and I called in on my way home for relief after a challenging day (and a purple haze in front of the eyes, as anyone who has been there will know) looking at the marsh orchids at Ynys Las.  Llynclys Common is a Shropshire Wildlife Trust reserve, and I found Greater among bracken and bramble, in small numbers but with no sign of Lesser or any hint of hybridisation.  

Llynclys Common where there is an old hybrid record

Greater

 So why is Cranham / Slad such a hotspot?  

A Paired Comparison of Pale and Magenta Forms of Green-winged Orchids

Two weeks ago my wife and I visited Eades Meadow in Worcestershire, which is a great place for Green-winged orchids.  They were just coming into flower, but it was noticeable that there were no pink or white plants, just the more normal magenta coloured plants.  Another member of a Facebook group dedicated to orchids to which I belong, visited a few days ago and found some white and salmon coloured plants.   It seems that they flower a little later than the magenta ones by a few days.

Do they differ in any other ways?  Are the pale ones bigger, or do they perhaps have more flowers.   To test this I went to Bernwood Meadows and later another BBOWT reserve, Pilch Field and made a simple paired study.  They are a bit closer than Eades Meadow.

Bernwood Meadows

Pilch Field

At Bernwood I estimated that the white and salmon pink forms were in a ratio of about 1:500 compared to magenta forms.  As a result there were only a few to be seen but of course they are very noticeable.  We paired up neighbouring plants. We selected a pale orchid and measured its height, number of flowers, the length of the spur and width of the labellum.  These measurements were then compared to those of the nearest magenta coloured plant. We ended up with 10 pairs at Bernwood, but only one at Pilch Field.   

Perhaps not surprisingly we found no differences between pale and magenta flowered plants; probably there is no difference but our sample size was small.  Intriguingly though the ratio of height to flowers for the pale plants was significantly different to that of the magenta form; the inflorescence was denser.  

The previous day I went to the private wood where I have permission to study a population of Greater butterfly orchids.  The day started well, with a group of hares in the arable field leading to the wood, )which I saw again on my way back to the car) and the orchids were in bud, though some were surprisingly spindly.   

In what has been designated the study area, last year there were 56 plants.  Their fate so far this year was as follows:

15 flowered last year - 9 in bud this year, 5 just in leaf, 1 no show

41 in leaf only last year - 10 in bud this year, 26 in leaf this year, 4 no show.

Greater Butterfly Orchid in Bud

Greater Butterfly Orchid in Bud

Bluebells

Hare - too fast for the camera(man)

I found and marked 30 new plants (one of which was in bud) were added giving a total of 81 plants showing either a bud or as a minimum a leaf.    A full count and measurement of height, leaf width, size of floral parts and number of flowers (if flowering) will be made in early June.   

Our Annual Orchid Count at Westwell Gorse

We went to Westwell Gorse, the BBOWT reserve south-west of Burford yesterday to repeat our count and measurements  this time last year of Early purple orchids   We have a  sample area which is unmarked but can be recognised by trees and bushes which we use as the boundary.  This year we counted 63 flowering spikes compared to 83 last year, due almost certainly to rabbits, the signs of which were very noticeable.  There were two or three chewed spikes on the ground.   On average the plants were shorter, (15.3 cm v 16.5cm, but the difference was not statistically significant.   The average number of flowers per spike was the same (9.8 both years).

 

We watched this sample area for 20 minutes just after noon in full sun.  During that period there were three insect interactions, one very brief.  One of the 63 plants was visited twice, surprisingly as it was only just breaking into flower.   The insects involved were all Rhingia campestris, not a known pollinator (The Flower of the European Orchid; Claessens and Kleynen), and indeed checking the plants involved, none of the pollinia had been removed.

The previous day I joined a recording group at Foxholes Wood, another BBOWT reserve, this time near Kingham.   As ever I found my patience and ID skills were well short of what was required, so I wandered off to see if I could find Herb Paris for which there are a few records.   I was not successful, and on rejoining the group they pointed me in the direction of some Early purple orchids which I had missed, growing in a damp shaded area by a stream, a complete contrast to the habitat at Westwell - grazed turf. 

      

Early purple and Green-winged Orchids: Not a hybrid in sight (Unsurprisingly)

Both Early purple orchid (Orchis mascula) and Green-winged orchid (Anacamptis morio) which are now in flower, are widespread and easy to find.  In the right spot there can be hundreds, even thousands.of plants.   Superficially they look rather similar, except that Early purples usually have spotted leaves, whereas Green-winged has unspotted leaves has but characteristic green veins on the two side sepals which form a hood.

They used to both be classified in the Orchis genus, but Green winged was split away, based on molecular evidence, and placed in the Anacamptis genus.   They both show significant, often attractive, colour variations from purple through to pink and white, but they do not seem to hybridise much with any other species.  There is though a hybrid between the two, Anacamptorchis morioides, which is an easily remembered name.   Unfortunately there are no records for this hybrid since the mid - 1970s on the BSBI database and only a handful before that, so what a challenge to find it and since there is less chance statistically of success than seeing the Ghost Orchid, Britain's rarest orchid (that at least appeared in 2009).

I started out by looking on the BSBI database for monads (1 km squares) where both orchids occurred in Oxfordshire and its surrounding counties, then looked at the individual records to see if they were close enough to be sympatric (ie grow close together).   I came up with 18 possible locations with the hotspot around Stroud in Gloucestershire (curiously also a hotspot for the Butterfly orchid hybrid).

Yesterday therefore I set off to that hotspot to share my day with golfers, dogwalkers (lots of them and the mess they leave - one woman had 9 dogs), horse riders and the odd off road cyclist, to look for the impossible, concentrating on orchids with spotted leaves and veined sepals.   Disappointingly the 1970s record is still the latest.

I started at Minchinhampton Common where both orchids grow quite close together, but only the Early purples were in flower. 

  

 I did find one orchid which I wondered about - unpotted leaves,spur a little less than 10mm and sepals gathered into a hood.  But there was no veining, so I concluded it was simply natural variation of a regular Early purple. 

                      

Then to Rodborough Common, a few miles north.   Here I could only find Early purples, though mixed up nicely with cowslips.

Though to the west, Selsey Common, proved more interesting.   Green-winged were more advanced and in places the two species grew very close together, the nearest being 20 cm apart. 

 But the numbers of both were small and there were no individuals with the slightest hint of hybrdisation.

 I spent quite a time watching a tachinid fly (I think, based on the wing pattern) thoroughly exploring a Green-winged orchid, waiting to see if it might, just might, detach a pollinia.  Sadly just as the moment approached, so did an uncontrolled, yappy dog which blundered into the orchid and the fly.   Harry was the dog's name I think, and imbecile that of the dog owner.