Albiflora studies in Ireland

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:

(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:

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.