Collecting Butterfly Orchid Measurements Together

The weather has not been inviting for a wander across the fields in recent days so instead I have been trying to find patterns in data that I have collected over the years.   In addition to the study Anne and I made of the butterfly orchids on Skye, and the ongoing work on a population of greater butterfly orchids in the Chilterns, whenever I find either of the two butterfly orchids I make measurements, as far as possible trying to get a random sample.  I used to restrict these to height, bottom leaf width, and the number of flowers, but I now take a flower photo - chosen at random - to measure the labellum length and width, the subtended angle between the pollinia,  the distance between the viscidia, the length of the lateral sepal and the angle of that sepal to the horizontal.

Greater Butterfly Orchid, Bald Hill 5.6.19

Lesser Butterfly Orchid, Cae Blaen Dyffryn 15.6.19

Hybrid, Warburg 16.6.19

I put all the data together, from 22 locations together with summaries from Skye and the Chilterns.
It includes some hybrids, mainly from Gloucestershire, but there is one from Warburg.  Altogether there are 224 observations for lesser and greater and 16 for the hybrid, (excluding Skye and the Chilterns studies) though not necessarily including all parameters for each observation

The data is very variable, but as might be expected there are clear differences between lesser and greater butterfly orchids, and indeed the hybrid.  A few examples of the averages (the differences have not been subjected to any statistical tests)

Ratio of  number of flowers to height
   LBO      0.70
   GBO     0.35 to 0.53
   Hybrid  0.69

Subtended angle between the pollinia
   LBO       4 degrees
   GBO     37 degrees
   Hybrid  15 degrees


Labellum width to height
   LBO       0.30
   GBO      0.24
   Hybrid   0.26

Spur length
   LBO      20.8mm
   GBO     27.1 to 33.8mm
   Hybrid  25.3mm

Spur length is dependent on latitude, but not to the extent I expected; the further north the shorter the spur, but shading also seems to have an  impact - shaded plants have longer spurs.  Plant height is affected by shading, but also by environment and latitude.   The Chilterns woodland greater butterfly orchids are taller than average, but have fewer flowers than would be expected for their heights.   Bald Hill, an open site, part of the Aston Rowant NNR, has stunted greater butterfly orchids yet is only a few miles from the Chilterns woodland site.   

The plant with the longest spur though was a hybrid from Warburg at 40mm (pictured above), reminiscent of long spurred orchids found in Holland, but as there was only 1 plant and it did not re-emerge this year, then all I can assume that it is simply a natural variation

Helleborines (Epipactis) in Fruit

Over the last few days I made a couple of trips to the Chilterns and one to a wood near Solihull to look for helleborines in fruit.  I found four species, dune, broad-leaved, green-flowered and violet.

I measured the fruit set success by counting the number of seed pods compared to the number of bracts in the inflorescence.  

	Fruit set	Fruit set
		Sample size
Dune	89%	9
Broad-leaved	89%	3
Violet	37%	1
Green-flowered	72%	2

Both dune and especially green-flowered, are self-fertilising.   Green flowered did not open out at flowering time, but nevertheless set fruit.  High rates of fruit set are therefore to be expected.  With green-flowered some of the flowers simply blackened and withered.

The fruit set % for violet helleborine is again to be expected; it is pollinated by bees and wasps, but it grows in deep shade, where wasps are not commonplace.  Higher fruit set rates are commonplace in mainland Europe though.   By contrast broad-leaved helleborine seems to attract every wasp from a distance around and that leads to a high fruit set.

Tree Wasp Pollinating Broad-leaved Helleborine in early August

These though were not random samples - I was attracted to the biggest and boldest in the case of broad-leaved helleborines, and later I did find a few plants where spikes had no seed pods.

Dune Helleborine

Green-flowered Helleborine

Broad-leaved Helleborine

Violet Helleborine

I then took averages of the seed pod width and length for each species and the angle that the seed pods are held from the vertical (facing up then less than 90°, facing down greater than 90°.   I finally brought a few seeds of each home and got an average for length and width.

	Seed pod		Angle	Ratio	Seed		Pod L;W ratio
	L mm	W mm	to Stem °	L:W	L mm	W mm	over Seed L
Dune	10.3	6.8	94	1.41	1.11	0.24	1.26
Broad-leaved	12.4	7.6	126	1.63	1.08	0.26	1.51
Violet	11.3	6.8	118	1.67	1.29	0.20	1.28
Green-flowered	10.2	6.7	157	1.54	1.06	0.19	1.46

The angle held to the stem is interesting, and is helpful in discriminating, as too is that final calculation - the pod length:width ratio divided by seed length.   This together with the angle to the stem, and leaf colour and dimensions should enable a helleborine to be identified to species level.  Of course though my sample size was far from statistically sound.

For the broad-leaved helleborines I also  worked out pod dimensions by the position on the inflorescence.

	Average	Average	Average	L:W
	Angle	Length mm	Width mm
Bottom Quartile	137	14.1	8.1	1.73
Lower Middle Quartile	123	13.0	7.7	1.69
Upper Middle Quartile	134	12.2	7.7	1.58
Top Quartile	113	10.6	6.9	1.55

The seed pods became smaller and less narrow moving up the stem, and were kept nearer to 90°.   I did not have enough measurements from the other three species but violet did not seem to behave in the same way.

I then ran out of things to measure! 

Orchids in Fruit at Yeosden Bank

Yesterday we joined the ANHSO field trip to Yeosden Bank in Buckinghamshire near Chinnor, one of the newer BBOWT reserves.    It was led by BBOWT's warden.  It is an area of chalk grassland with a small area of woodland - ash and beech.   In the grassland were lots of  Chiltern gentians (Gentianella germanica)  and Small scabious (Scabiosa columbaria).   At the woodland edge there were dense patches of Devil's-bit scabious (Succisa pratensis).   To some the latter is quite a novelty, but from my time on Skye I remember it as one of the commonest plants, found in almost every tetrad on the island. Whereas to me, Chiltern gentian is worth getting excited about!

Chiltern Gentian

Small Scabious

Devil's-bit Scabious

Yeosden Bank has several orchids and I thought I would try to identify spikes based on appearance, leaves if extant, seed pod dimensions and the angle of attachment of seed pods to the stem.   I think I found examples of three orchids, Common spotted, (Dactylorhiza fuchsii), Pyramidal  (Anacamptis pyramidalis) and Chalk fragrant (Gymnadenia conopsea):

Probably common spotted:

Seed pod length 9.5 mm width 4.2 mm
Angle of attachment 29 degrees

Probably common spotted:

Seed pod length 7.7 mm width 2.7 mm
Angle of attachment 37 degrees

Probably chalk fragrant:

Seed pod length 7.4 mm width 2.6 mm
Angle of attachment 11 degrees

It is getting a bit late in the year for butterflies, but were numerous butterflies still to be seen though many were worn.  Amongst the fairly battered Common Blues, I am pretty sure this is a fairly battered Adonis Blue. 

A mammal stole the show however  - a hare running up the bank.   As ever only a fleeting glance - and much too fast for a  photo opportunity.  They are such a treat to see.

Autumn Lady's-tresses close to home

North Oxfordshire, sitting on ironstone and clay, is not rich in orchids.  The nearest reliable sites from Hook Norton are more than 15 miles away.

Well that has all changed - ok, just a bit.  Last year the joint vice county recorders for Northamptonshire, found a single plant (?) of Autumn Lady's-tresses in Banbury (it's in the administrative county of Oxfordshire but the botanical vice-county of Northamptonshire, so they weren't trespassing).   A  mere 11 miles from Hooky, I went to the site yesterday to see for myself.  Its on an industrial estate to the east of the town centre which was part of the expansion of Banbury alongside the M40. 

There were 6 flowering spikes in all, though one was damaged, on a landscaped road verge, which fortunately had not been mowed for two or three weeks.   Only in the one place though possibly because other verges are kept mown rather more regularly.   My priority now is to try to convince the owners and maintenance contractors to restrict mowing until after tha plants have fruited.

Rare Arable Weeds

Taking a break from searching for helleborines which has been my focus for the last 3 weeks, on Saturday I joined the Wychwood Flora Group's annual survey for Red Hemp-nettle (Galeopsis angustifolia).  It's rare, described as nationally critically endangered.  There is one consistent location a few miles south of Chipping Norton in the headland of field near Lidstone, which because of the farmer's interest, never gets sprayed.  The vast majority of the Oxfordshire records are from there.

Growing up in the Lake District where farmland is either pasture or was at one time hay meadows, I had never seen arable weeds until I moved south, so they are a bit of a novelty for me.   On Saturday there were probably more plants there than had been seen for a long time - robust, branched, growing up to 30 cm.   Stunning, and not difficult to find.

Red Hemp-nettle

Red Hemp-nettle

Red Hemp-nettle

There were other interesting plants such as  night-flowering catchfly (Silene noctiflora), - scarce in Oxfordshire - and because we started out quite early, the petals were flat and white (arguably a very pale pink), rather than curled over to reveal the creamy underside, causing much confusion, mainly initiated by me because in a field at Coldharbour a couple of weeks ago I saw plants just as they should be so at Lidstone I was rather dogmatic about curled over creamy petals!.   Other nice things included round-leaved fluellen (Kickxia spuria) and dwarf spurge (Euphorbia exigua).

Night-flowering catchfly

Night-flowering catchfly

Night-flowering catchfly, Coldharbour Farm in the afternoon

Round-leaved Fluellen, Coldharbour Farm

My Hill's Herbal, 1812, gives an alternative name for the fluellen as Elatine and notes that the juice is cooling and astringent, though collecting a usable quantity from this little weed would seem to be quite a challenge.

Meadow clary (Salvia pratensis)

A quiet weekend near home after a trip north last week to join a  Skye Botany Group walk over the limestone pavement at Torrin where the highlight for me was dark red helleborine in leaf (others found the sedges more exciting!), and  Aviemore for coralroot orchid among other nice things, 

Heath Fragrant Orchid at Torrin

Small White Orchid, North Skye

Coralroot Orchid, Aviemore

Coralroot Orchid, Aviemore

Meadow clary is a nationally scarce native which has a stronghold in North Oxfordshire, particularly an area around Charlbury on the oolitic limestone.  Quoting from 'Threatened Plants of Oxfordshire' it prefers waysides and ancient grasslands on chalk and limestone, with perhaps raised magnesium levels.  Seed generates readily but not in close sward.

Described as nationally near scarce, in Oxfordshire it is not so, if you know where to look.   For many years the Wychwood Flora Group (originally the Cotswold Rare Plant group) has been monitoring most of the populations and undertakes an annual census.   I joined the survey of three sites on Saturday; it proved to be very worthwhile, not only to see the meadow clary because in addition we came across a wasp orchid (Ophrys apifera var. trollii) on a road verge near Crawley.   On the same verge was a single plant of cornflower, now a rare arable weed, growing on ground disturbed by cable laying, and almost certainly not introduced, together with long-stalked crane's-bill, both of which are covered in 'Threatened Plants of Oxfordshire.

Wasp Orchid

Wasp Orchid

Long-stalked Crane's-bill 

Pyramidal orchid var. albiflora

Pyramidal orchids

We found lots of pyramidal orchids, including a couple of pure white plants (var. albiflora) some normal bee orchids and inevitably common spotted orchids.

Yet the best is still to come.  On Thursday evening another location will be visited - near Fawler - which has thousands of meadow clary plants including white forms, and is probably the best site in the UK.  Even better there is a good pub not far away too for later.

Annual greater butterfly orchid counts in the Chilterns

A busy week.   I made a counts of greater butterfly orchids in 3 Chilterns locations.   At Greenfield farm there are around 500 plants, with 196 flowering spikes last year.  The plants are in two enclosures, fenced to keep out deer.   Plants are spreading outwards beyond the fences.   This year, the third, I counted all the plants, flowering and non-flowering, in the South enclosure but because the sward - dog's mercury, cleavers and nettles - was so dense in one area, I only counted flowering spikes in the other, North, enclosure.   And it rained. 

Both enclosures are shaded by young beech and ash, but because the ash has succumbed to die-back, light levels are increasing.   During the winter bramble was cut back and then in March I used a brush cutter to limit the dog's mercury in the North enclosure, though I don't seem to have made much impression on it. The heavy sward is choking out the orchids there.  

Sub-section with all plants marked

Almost ghostly in the early evening

  

A statuesque  greater butterfly orchid

The number of flowering spikes was dramatically less than last year; there were only 65 compared to 196 last year.

Snails were a significant problem in early April, so that this week plants that had been damaged then looked very unhappy, and the effect will probably be seen next year also because tuber growth will be impaired because of the leaf damage.  In one sub-section where I made detailed measurements of all the plants over a third of the plants had serious leaf damage, and the number of plants 'lost' i.e. nothing showing, was roughly a third of the total plants there last year, a rate of attrition far higher than we have seen in the last 2 years.

Leaf damage by snails

The enemy.

Winter was mild; and I wonder if this has led to a big increase in the number of snails.

Another possible cause of the fall in numbers might be climate.   The early autumn last year was very dry.   Could this have constrained tuber development and the ability of plants to flower?   Lots
of analysis to do in dark winter nights!

I made a count of the flowering spikes at Bald Hill, part of the Aston Rowant NNR.   A simple traverse but the same as last year, gave me a total of 18 flowering spikes, compared to 26 last year.  Unlike Greenfield these are plants out in the open, and although the reduction in numbers in percentage terms was not as great, it was noticeable that the plants were small.  One blessing was that it did not rain.

The third count of the week was of the butterfly orchids at Warburg NNR, the BBOWT reserve.   There it really did rain, so much so that my pocket voice recorder got damp and gave up on me and my waterproof clothing proved to be anything but.   I have yet to complete the analysis of the count but numbers there were also down on last year.   For instance I could find only 1 flowering lesser butterfly orchid (4 last year)  and I could find no greter butterflies on one of the rides where there had been several last year.

Lesser butterfly orchid

I did though find 3 bee orchids (in the rain inevitably).

Bee orchid

Looking for an intergeneric hybrid more in hope than expectation

I still have not given up on the search for the putative intergeneric orchid hybrid - the cross between Green-winged orchid (Anacamptis morio) and Early purple orchid (Orchis mascula).  I am very doubtful, as is much of the literature, about whether it exists in the wild in Britain though there are a few, old, records on the BSBI database, the most recent from 1985 from Arnside made by a reliable recorder, and recently I saw a picture of this plant. Even so, I am not sure if I was convinced.   

Both are pollinated by bees, including bumblebees, but both show low rates of pollination success (20 to 30% seed set for Green-winged and around 10% seed set for Early purple), not surprising perhaps given that they flower early.   In addition there are possibly reproductive barriers to cross fertilisation.

Last Sunday I went to Minchinhampton Common and then to Selsley Common in Gloucestershire where both are intermingled looking for plants that ideally had spotted leaves (characteristic of early purple, though not always) and veining on the sepals (characteristic of Green-winged) even if just a hint.   I found nothing, and so to another site yesterday near Snowshill, around 20 miles from Hooky, to what looked like an old quarrying area.   The same story, despite looking at perhaps more than a hundred plants - at least - where both parents were close together, dwelling on a handful, but concluding that they they fell on one side of the fence or the other.  

Early Purple Orchids

Early Purple Orchids

Green-winged Orchid

Green-winged Orchid

A few colour variations of both were interesting but the highlight undoubtedly was the twenty or so plants of Pasqueflower (Pulsatilla vulgaris) and lots of Meadow saxifrage (Saxifraga granulata).

Pasque Flower

Pasque Flower

Meadow Saxifrage

Meadow Saxifrage