Most orchid species don’t like acid boglands – but there are two rare exceptions: One is geographically widely distributed from Belgium to Northwestern Germany and Scandinavia and is mostly addressed as Dactylorhiza sphagnicola. The other grows only in the Danish region of Thy: Just a few hundred meters behind the coastline of the North Sea there is a population of white-flowered orchids which have been described by Henrik Ærenlund Pedersen as Dactylorhiza majalis subsp. calcifugiens (in: Nordic Journal of Botany, 2004). In 2007, Sebastian Sczepanski and Karel Kreutz argued it would be more appropriate to regard these plants as a subspecies to Dactylorhiza sphagnicola – while Pedersen und Mikael Hedrén are viewing sphagnicola only as another subspecies of Dactylorhiza majalis. Apart from colour, the morphological differences of the single flowers of Dactylorhiza majalis subsp. majalis (left), calcifugiens (middle) and sphagnicola (right) are difficult to discern:
src="http://www.albiflora.eu/images/science/majalis_calcifugiens_sphagnicola_sm.png" alt="Dactylorhiza" />The spur of Dactylorhiza sphagnicola is a bit longer than that of D. majalis subsp. calcifugiens. And the leaves of the latter are spreaded in a broader angle than those of D. sphagnicola:
The single flowers don’t show any hue of purple, even the pollinaria lack Anthocyanin. There is rather some yellowish hue in the center of the flower, slightly reminding of Dactylorhiza incarnata subsp. ochroleuca. In contrast to other populations of albiflora forms, e.g. with Dactylorhiza fuchsii, there are no gradual differences in the loss of colour pigments – all the plants are consistent in the white colour of their flowers.
Visiting the region, I found calcifugiens at two places, one near the small fisher village of Lild Strand with only three plants, the other further to the south at a bog called Nissekaer with about 150 plants. Surrounded by dunes this place is a natural depression (danish: “kaer”) with a length of about 1500 and a width of about 250 meters:
In mid-June the orchids are just in the beginning of flowering. Most Dactylorhiza majalis subsp. calcifugiens are growing at the edges of the wet places, not in the midst of them as it is the case with Dactylorhiza sphagnicola in the Venn moors in Belgium. And the calcifugiens plants are quite smaller, reaching just a height of up to 31 cm. Neighbouring plants are Sphagnum palustre, Equisetum fluviatile; Eriophorum angustifolium, Menyanthes trifoliata, Vaccinium oxycoccus, Calluna vulgaris, Trientalis europaea and even Drosera rotundifolia – most of those plants are clear indicators of acid soil. Among the shrubs there is the dominant Myrica gale, which is used by the brewery of the near-by town Thisted.
Some calcifugiens plants show a broader labellum, indicating a possible hybrid influence of Dactylorhiza maculata – similar to the sphagnicola plants of the Venn region.
Among all the white-flowered orchids in the Nissekaer bogland I found two purple-flowered plants which might be a hybrid of Dactylorhiza majalis subsp. calcifugiens and Dactylorhiza maculata (left) and a Dactylorhiza maculata still in buds (right):
As a visiting and possibly pollinating insect of Dactylorhiza majalis subsp. calcifugiens there was a species of the genus Syrphida – as I’ve seen also with Dactylorhiza sphagnicola in the Venn moor (left)
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In addition to the Irish region of The Burren and the Hesse location of Biebergemuend there is a further location where Dactylorhiza fuchsii tends to white-flowered forms in big numbers: In a birch grove near the village of Wolken in the upper Moselle valley there are several hundred plants with a clear trend to bright and white flowers. A count of a random sample resulted in 13 per cent of white flowers without any markings on the labellum. Further 38 per cent of the plants have a white base colour with pink marks. The differences in flower colours correspond with the results found in the other two regions and are even a little bit more accentuated. These results may give further evidence to the assumption that Dactylorhiza fuchsii is in the midst of an evolutionary process which also changes the phenotype of the species.
Percentages of flower colours in different locations
The following tableau shows the wide range of fuchsii flowers found on that location. The brightest forms also lack the Anthocyanine pigments in the pollinaria as the lowest row of examples and the following macro photo demonstrate.
The only other orchids in the forest are Platanthera chlorantha and an Epipactis spec. – while in the other two locations with abundant albiflora forms of Dactylorhiza fuchsii there are also the earlier flowering Orchis mascula (Burren) and Dactylorhiza majalis (Biebergemuend), both flowering in pink and both – as well as Dactylorhiza fuchsii – trying to attract pollinators with nectar deception. Among other plants in the birch forest, a former gravel-pit and now a nature reserve called “Kuhstiebel”, are Orthilia secunda, Fragaria vesca and Tussilago farfara. But the dominating plant there as well as in a nearby marsh area is Dactylorhiza fuchsii with mostly spotted leaves – even in the case of the white-flowered plants:
Two specialists of the orchid flora on Corsica, Wolfram Foelsche and Klaus Cord-Landwehr, have described a new Dactylorhiza species: Dactylorhiza cyrnea belongs to the group of Dactylorhiza maculata and shares its characteristics of a tetraploid set of chromosomes. In their article “Dactylorhiza cyrnea und die Taxa der Gattung Dactylorhiza auf Korsika”, published in the Journal Europäischer Orchideen (Vol. 44, Heft 1, April 2012), the authors review the findings of Dactylorhiza insularis, Dactylorhiza sambucina and Dactylorhiza saccifera on Corsica and note that there is no Dactylorhiza majalis confirmed for this Mediterranean island. The plants described as Dactylorhiza cyrnea is morphologically similar to the diploid Dactylorhiza fuchsii. They are rather elongated and grow in humid locations. The leafs are mostly vaguely spotted but may also be unspotted. The flowers have a markedly thin spur (contrasting the thick spur of D. saccifera) which is shorter than the ovary. Their colour is a bright pink, with a purple labellum pattern. The population described by the authors “offers a very consistent appearance” – but there are also white flowered plants occasionally, the authors note. The photo above on the right, generously sent to me by Wolfram Foelsche, is also included in the article.
Invited by the Arbeitskreis Heimische Orchideen (AHO) Rhineland-Palatinate I’ve presented some thoughts about albiflora orchids at a meeting in Koblenz. After introducing the basics of the bio-chemistry and genetics of flower colours I pointed to the striking differences in the frequency of albiflora forms with certain orchid species. With frequencies of more than 0.1 per cent one might assume that albiflora forms are not just the result of spontaneous mutations but may indicate a certain evolutionary process. With regard to Dactylorhiza fuchsii there is reason to believe that there are ecological pressures favouring albiflora forms – a hypothesis, which will be elaborated in an upcoming article in AHO’s journal “Berichte aus den Arbeitskreisen Heimische Orchideen”.
Still looking for any hints to shed some light on the albiflora phenomenon, I visited Richard Bateman in London. The white-flowered morphs “are of greatest interest to me because of their relative frequencies in the diploid and the tetraploid groups of Dactylorhiza”, he told me. “If your mind works its ways through the different diploids – incarnata, fuchsii, sambucina – they all show colour polymorphism. And they all have a certain number of very pale or white individuals.” Quite different are the observations with tetraploid Dactylorhiza species like praetermissa, majalis or alpestris. Bateman noted: “I’ve only found one albino praetermissa and one albino traunsteinerioides in 30 years of going in the field.” Quite younger is the albiflora.eu project – but up to now only some scattered findings of white-flowered Dactylorhiza majalis have been reported – and none of praetermissa or traunsteineri. As a possible explanation Bateman noted: “Presumably, in the tetraploids there has to be a minimum of four copies of a gene that is malfunctioning to cause the albinism. So I think the tetraploids are buffered against albinism by having additional copies of the genes that generate the anthocyanin pigments.”
Arguing with him about the negative connotations of the term malfunction, Bateman answered: “Most organisms are ‘designed’ to remain the way they are and not to change [substantially]. So, from a genetic viewpoint, any change that is expressed is a malfunction. I agree the malfunction could be beneficial rather than negative but most times it’s negative.”
Bateman’s main interests in research are the questions of speciation or at least the question of what might lead to evolutionary divergence between populations: “The genus level – for me at least – is solved. The species level interests me the most now. That’s were the most challenging topics still have to be addressed – how orchids speciate.” Despite a huge literature on the topic, Bateman noted, those questions are still not adequately solved. “Each time I address a particular set of orchids, the answer [to this question] is different.” So up to now, no generalization is possible. But, Bateman said, “I strongly believe that the importance of pollinator [specificity] is being exaggerated by a lot of workers.”
At least one general observation can be stated according to Bateman: “New [evolutionary] strategies are tried out constantly – more than most people believe – but I think they succeed less often than most people believe.”
In addition to such reflections on stability and change in the genetics of orchids, we wondered why hypochrome forms of Ophrys are rather green than white – obviously the Ophrys flowers still contain chlorophyll even if they lack the anthocyanins – and with good reason: “The rosette leaves of Ophrys (and Himantoglossum as well) tend to be dead before the flowers properly open”, Bateman said. “So I don’t think there is much supply of nutrient coming from [root to flower]. The flower has become autonomous … whereas in Orchis or Anacamptis the flowers are far less independent.” So, Ophrys flowers are quite special. “One of the most striking things when you start working on the flowers, cutting them up looking at them under microscope, you realize how much energy is invested in an Ophrys flower. There is a lot of tissue.”
After the visit, the Royal Botanical Gardens in Kew have been the very right place to further contemplate on the miracles of nature. (With thanks to Richard Bateman for reviewing his quotes, additional notes are marked with brackets)
Form and function of the flower organs are the main focus of the new fascinating book The Flower of the European Orchid by Jean Claessens and Jacques Kleynen. Illustrated by great macro as well as microscopic photos this important opus presents a comprehensive description of the structure of orchid flowers with the different European genera. In a foreword, Richard Bateman writes: „No other family of plants can match the orchids for their sheer charisma“. But the excitement goes along with a certain scientific pain – Bateman stresses that there still remain major scientific uncertainties which „further torment us“ – among them questions of evolutionary adaptation.
The orchids’ strategies of fertilization are manifold and the book explains how the specific construction of the column (gynostemium) supports allogamy by pollinators or autogamy (self-fertilization). Especially intriguing are the strategies of Dactylorhiza, Orchis and other genera without any nectar in the spur. Claessens and Kleynen explain that the pollinators of Orchis mascula are „recently emerged, naïve bees or exploratory insects that have not yet learned that the flowers offer no reward” (p. 220). The authors also cite the study of L. Dormont, R. Delle-Vedove, J.-M. Bessière, M. Hossaert-Mc Key und B. Schatz about the presence of white-flowered Orchis mascula which underlines „the importance of visual cues for attracting pollinators“ (p. 220).
In the Dactylorhiza chapter the authors write: „Colour can also influence pollinator behaviour“ (p. 240). With regard to the red and the yellow forms of Dactylorhiza sambucina they refer to experiments showing that experienced bumblebees „preferred by far the morph that most resembled the rewarding plant on which they have fed previously“. Vice versa it may be presumed that there may be a form of evolutionary adaptation directed to develop visual cues which are different from non rewarding plants being abundant in a certain region – as it could be the case in Western Ireland with the many white-flowered forms of Dactylorhiza fuchsii on meadows with earlier flowering Orchis mascula.
Similar to The Burren there are also some continental locations where Dactylorhiza fuchsii tends to develop white or at least bright flowers. In the Belgian province of Liège, near Lanaye, there are dozens of albiflora forms of this species, as Jeroen Gerdes told me – he sent me the photo at the left.
Today I visited a meadow near Biebergemuend in the Hesse part of the mountain range called Spessart. On a space of about 5,000 square meters I counted about 300 Dactylorhiza fuchsii with the following distribution of flower colours (in per cent):
|Dactylorhiza fuchsii with||%|
|dark pink flowers||2|
|medium pink flowers||6|
|bright pink flowers||45|
|white flowers and labellum marking||44|
|white flowers without marking||3|
In total 10 of about 300 Dactylorhiza fuchsii are albiflora forms – such a frequency is quite higher than usually observed with this or other orchids species and leads to the assumption that there might be some gradual or saltational evolution under way.
Among the other plants in this area I noted Dactylorhiza majalis (withered), Dactylorhiza fuchsii x majalis, Platanthera bifolia, Neottia ovata, Rhinanthus minor, Cirsium arvense, Campanula persicifolia, Picris hieracioides and Arnica montana. Dactylorhiza majalis grows in the neighbourhood of wet ditches along the meadow – and there are also hybrids of D. majalis and D. fuchsii – still flowering while D. majalis is already withered. The hybrids are rather strong, some of them with a height of up to 50 cm. They can easily be determined by their broad leaves and the rounded labellum of the flowers with a reduced medium lobe. There is also an albiflora form of Dactylorhiza fuchsii x majalis (right).
The evolution of certain orchid species is far from being finished. The Burren, a region in County Clare at the Western coast of Ireland, illustrates this fact by its manifold colour varieties of Dactylorhiza fuchsii. In 1988, R.M. Bateman and I. Denholm, came to the result that the Burren populations of Dactylorhiza fuchsii show more often a lack of the purple pigment anthocyanin than plants in other regions of the British Isles:
|Percentage of Dactylorhiza fuchsii lacking||Burren||other regions|
|all floral anthocyanins||35||8|
|all anthocyanins in flowers, stem, leaves and bracts||25||6|
(Source: R.M. Bateman/I. Denholm: A reappraisal of the British and Irish dactylorchids, 3. The spotted-orchids. In: Watsonia 17 (1988), p.332)
When exploring the fascinating area around the Lough Gealain and the Mullaghmore mountain these results seem to be quite realistic. In other areas as well there are many plants, which have bright or white flowers but still retain anthocyanins visible in the markings of the labellum. In a limited area of 40 square meters in the region of Rockforest, northeast of Corrofin, I counted 50 flowering Dactylorhiza fuchsii (in addition to 7 with buds) with the following characteristics:
|Dactylorhiza fuchsii with|
|dark pink flowers||0|
|medium pink flowers||11|
|bright pink flowers||17|
|white flowers and line markings||3|
|white flowers and dot markings||17|
|white flowers without markings||2|
Among the other plants in this area in the middle of a vast limestone pavement there are Orchis mascula, Geranium sanguineum, Rosa pimpinellifolia, Calluna vulgaris, Lotus corniculatus and Pteridium aquilinum.
The following image illustrates the broad variety not only of colours but also of the labellum forms of Dactylorhiza fuchsii in The Burren (some of the examples obviously showing a certain introgression with Dactylorhiza maculata). It becomes clear that most plants have less floral anthocyanins than continental populations of the species – for example the large forest populations in the French region Causses with its deep pink flowers. The pigments are first reduced in the sepals. This reduction continues in the base colour of the labellum. Then the markings of the labellum are reduced, often only a small rest is retained at the mouth of the spur. Even the very white flowers still have coloured pollinia but their colour is less intense. There is also a wide variety of labellum forms. Especially the central lobes largely differ. And there is the extreme case of a white flowering plant whose lateral lobes are reduced to a minimum (lowest row in the middle).
Most Irish and British botanists stress that the Dactylorhiza fuchsii var. okellyi (some authors view this as subspecies or even as species) must not be mixed up with the albiflora forms of fuchsii. Anne and Simon Harrap (Orchids of Britain and Ireland, 2005) are writing: “A lot of controversy surrounds okellyi” and explain: “In The Burren and elsewhere these classic white-flowered okellyi are just part of a population of plants with a variable flower colour”. Brendan Sayers and Susan Sex (Ireland’s Wild Orchids, 2008) stress that Dactylorhiza fuchsii var. okellyi flowers late, beginning in July. The photo in their field guide shows a flower with a labellum, which is deeply divided into three lobes. Charles Nelson (Wild Plants of The Burren and the Aran Islands, 2008) indicates that Dactylorhiza fuchsii f. okellyi flowers from June to August and has pure white flowers “without any pink tints or marks” and a “lip flat with 3 almost equal, deeply-cut lobes”. According to Pierre Delforge (Guide des orchidées d’Europe, 2005), who mentions a flowering period from May to July, the labellum has a maximum width of 8 mm (in contrast to fuchsii with 8-16 mm). Pat O’Reilly and Sue Parker (Wild Orchids in The Burren, 2007) have noted that “groups of pure-white orchids … are more likely to be O’Kelly’s Spotted-orchids than single plants, which might be just very pale examples of the Common Spotted-orchid”. When exploring the limestone pavements between Poulsallagh and Rockforest you’ll find lots of white-flowered Dactylorhiza fuchsii, rather small and with a pyramidal spike in the beginning of flowering, which are very similar to pink-flowered plants of the species – they should be considered as albiflora forms. Two times I found a pair of taller plants, very slender and with a distinct appearance of spike or flowers, which could be addressed as Dactylorhiza fuchsii var. okellyii.
Dactylorhiza maculata also tends to develop very pale flowers in The Burren. But most of them retain at least a faint marking on the labellum. The variety of Dactylorhiza maculata (the plants in Ireland are in general addressed as Dactylorhiza maculata ssp. ericetorum) seems to be not so wide as the variety of Dactylorhiza fuchsii. The relative frequency of Orchis mascula f. albiflora is in the same range as in continental Europe. Among thousands of plants – Orchis mascula being the most frequent orchid of the region – I’ve seen just two white ones. And there wasn’t one single albiflora form of Dactylorhiza incarnata or Dactylorhiza majalis ssp. occidentalis (on the Aran Island of Inisheer).
Compared with the relative stability of the other plants, the broad variability of Dactylorhiza fuchsii in The Burren clearly shows that this species is still in a state of an ongoing evolutionary process. It can only be speculated why Dactylorhiza fuchsii in The Burren prefers brighter or even white flowering – in the midst of an abundance of pink and purple flower colours on the meadows of the region.
Studying a marsh with about 2,000 Broad-Leaved Marsh Orchids (Dactylorhiza majalis) at the Southern edge of the Rhoen region in Germany I saw a group of three albiflora plants together with Menyanthes trifoliata, Caltha palustris and other marsh plants. Even more interesting was another albiflora plant in a distance of about 40 meters with an orchid in its direct neighbourhood showing a kind of partial albiflora: Most of its flowers have the standard purple colour but some flowers are partly purple, partly white – either in the lip or in the petals.
Obviously, the genetic allele containing information for the albiflora form has plaid a certain role for this plant – but it was dominated by the DNA, which contains the information for the standard colour. This observation as well as a similar one in Southern France with Anacamptis morio poses questions about the recessive character of the albiflora allele. There might be some cases where the albiflora allele of one parent plant is not totally restrained by the dominant purple allele of the other parent plant which results in such purple and white spotted flowers. Before I continued the trip to a charming meadow with hundreds of Anacamptis morio (among them two albiflora) and Orchis mascula I made use of the rising morning sun to make some more photos of the Dactylorhiza majalis f. albiflora trio:
In an e-mail exchange following his recent article in the Journal Europaeischer Orchideen (JEO), Richard Bateman, orchid specialist at Kew Gardens, wrote me that albiflora plants “are far more common among diploid Dactylorhiza species than tetraploid species”. A possible reason might be the “buffering of mutations by having four comparable genes in the tetraploid chromosomes”. Diploid species (with 40 chromosomes) are Dactylorhiza fuchsii, D. incarnata and D. sambucina. Tetraploid species (with 80 chromosomes) are D. majalis, D. praetermissa, D. maculata, D. elata, D. sphagnicola and D. traunsteineri.
Albiflora plants of Dactylorhiza fuchsii are quite often observed, and in Ireland there is also the intriguing D. fuchsii ssp. okellyi which is diploid as well. D. incarnata and D. sambucina are known for their colour dimorphism: red and yellow with D. sambucina, purple and yellowish-white with D. incarnata and its var. ochroleuca. In a recent article in the Annals of Botany (2009), Mikael Hedrén and Sofie Nordstroem presented the results of their reasearch about the colour dimorphism with D. incarnata. They observed that there was “no clear pattern of habitat differentiation … among the colour morphs”. With D. incarnata var. ochroleuca “the lack of anthocyanins is probably due to a particular recessive allele in homozygous form” – the diploid chromosome set has both alleles determining the lack of purple in the flowers.
Besides genetics, colour also affects the pollination function of orchid flowers. Bateman wrote me that “in at least a few cases, instantaneous loss of anthocyanins (or even just radical decrease in anthocyanin production) must affect pollinator preference, and lead to lineage divergence”. A potential example of such an evolutionary process could be Gymnadenia frivaldii as a relative of Gymnadenia conopsea.
But in general the question of a certain functionality of colour change is still unanswered. Following his mentioning of white flowers in the above mentioned JEO article, Bateman wrote me it would be “more correct to use the term ‘parallelism’ rather than ‘convergence’, since in most cases no-one has demonstrated a change of function or ‘behaviour’ in the abnormal white flowers”. He further noted “the probability that many different mutations and epimutations generate white flowers”. Recognising that there are quite many open questions, Bateman also asked “whether white is actually a colour at all”, pointing to the “very simple shifts between ‘white’ flowers and ‘green’ flowers in Platanthera”.