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Orthilia secunda (L.) House, Serrated Wintergreen

Account Summary

Native, very rare and conservation protected under Schedule 8 of the Wildlife (NI) Order 1985. Circumpolar boreal-montane.

26 June 1901; Tetley, W.N.; N-facing sandstone scarp at the SE end of Correl Glen.

Throughout the year.

Growth form and history in Ireland

This is an extremely rare, evergreen, rosette-forming, creeping rhizomatous perennial in Ireland and it has been so for many years. It became extinct at its previous Co Offaly (H18) bogland site (destroyed by peat cutting in the 1950s), and has not been seen at a previous site in Co Londonderry (H40) since 1888. There were five stations in Co Antrim (H39) with dates in the early 19th and early 20th centuries and it had not been seen at any of them since 1920 until RHN rediscovered it on the bank of the Cranny Water in 1996 (Irish Red Data Book; Northridge & Northridge 1997).

Fermanagh occurrences

In Fermanagh, O. secunda sometimes occurs in dense clonal patches and considerable quantity, in crevices and on ledges on dolomitized sandstone scarps and scattered in steep, submontane, mossy, Calluna-Vaccinium-dominated heathy slopes below these cliffs on the Western Plateau (ie in the Lough Navar Forest Park area). When one has got one's eye in for it, the rather pale, grey-green, wintergreen, serrated leaves can be picked out amongst other foliage and moss all year round. All 59 Fermanagh records are concentrated within one 10-km square (H05) and they can be mapped as nine tetrads, 16 1-km squares or 31 100 m squares!

The plant still occurs in Tetley's original 1901 site on drier sandstone ledges on the lower half of the sandstone cliffs at the bottom end of the Correl Glen NR (Praeger 1901b). This is the only spot in Fermanagh where the species grows under trees (ie in upland mixed deciduous woodland with oak and birch), rather than under subshrubs, Calluna vulgaris (Heather) or Vaccinium myrtillus (Bilberry) (Praeger 1903c). Since the whole area where O. secunda occurs is on the Western Plateau, it should be understood that what Praeger described as, "drier ledges in the Correl Glen sandstone scarps", still represents very damp, humid conditions – given the prevailing high rainfall figures in the locality and the sheltered, wooded, gully-like nature of the lower (ie the southern) end of this deep wooded glen.

Flowering reproduction

Serrated Wintergreen flowers very sparingly in Fermanagh, somewhat less than 10% of rosettes bearing an inflorescence. On the evidence of Praeger's descriptions of it when it was first discovered by Tetley, West and himself (Praeger 1903b, 1904), RHN and the current author (RSF) reckon there has been a marked decline in flower and rosette frequency during the last century. The account of O. secunda by Dr D.A. Ratcliffe in Scarce Plants in Britain (Stewart et al. 1994), very closely matches the Fermanagh situation described here, both in terms of habitats occupied (apart from rocky stream banks) and marked species decline in abundance and flowering capacity.

The characteristic secund (ie one-sided) raceme inflorescence develops in July and August and consists of between six and twelve cream or whitish-green, bell- or funnel-shaped flowers, each of which persists for up to a week. The flowers do not have any scent (at least none perceivable to the human nose!), but they attempt to attract insect visitors by providing food in the form of both nectar and relatively large amounts of pollen.

In a study of flower biology carried out in Denmark, Knudsen & Olesen (1993) found that O. secunda attracted bumblebees both as nectar-collectors and to a lesser extent as pollen-buzzers. The anthers of Pyrola and Orthilia species release their pollen through restricted openings or pores and the bee visitors carry out 'buzz-pollination'. This involves the bees gripping an anther and using rapid contractions of their indirect flight muscles to vibrate or 'sonicate' them and they then harvest the pollen shower this process releases (Knudsen & Olesen 1993)

The flowers are strongly protandrous, the anthers opening a few days before the flower fully opens, the stigma only becoming receptive one or two days after anthesis. The Danish study found that in untreated bagged flowers (ie autodeposition of pollen) only 0.5% of their ovules set seed, while under uncontrolled unbagged conditions (ie open-pollination) 84% of ovules set seed. Unfortunately, however, the experiment did not investigate self-compatibility, since the ability to self-fertilize is probably important in O. secunda as is the case in many of its relatives. In addition, general observation indicates that insect visitors are infrequent to rare in the damp, shaded, upland habitats in which O. secunda grows (Knudsen & Olesen 1993).

Seed production

About mid-September the ripe fruit capsules open to release the numerous tiny seeds (Helenurm & Barrett 1987). Measurements made in Britain by Salisbury (1942, p. 95) found that O. secunda seed production was of the order of 3,500 (± 500) per inflorescence. Since the species normally has a branched rhizome, however, each genome bears several inflorescences. In species of the closely related genus Pyrola, the branched rhizome is more fragile than in O. secunda and the underground connections between the leaf rosettes usually do not persist, so that separate individual ramets arise. This does not happen in O. secunda. O. secunda seed is even smaller than that of British orchids and it is light enough to be carried aloft by the slightest breeze.

Little or nothing appears to have been published on the reproductive ecology of O. secunda and the current writer could uncover absolutely no information on seed germination requirements, season or seedling establishment and nothing on the competitive ability of the species − all clearly important in reaching an understanding of the ecological future of the species in B & I. There are two references regarding seed survival in the soil seed bank, both Russian and indicating that it is only transient (Thompson et al. 1997).

Seed germination and lack of establishment

A mycorrhizal fungal partner is required for successful germination and establishment, but observations of the behaviour of the species in the last century in both Scotland and Ireland, strongly indicates that little or no colonisation of fresh sites by seed is taking place (D.A. Ratcliffe, in: Stewart et al. 1994). However, O. secunda can reproduce vegetatively and it has managed to survive, although certainly not in the same abundance as Praeger described, at or very close to all but one of its early 20th century Fermanagh stations. The exception is Praeger's 1904 site on the cliffs E of Glencreawan Lough (Praeger 1904) described in IN 13: p. 239, as, "North of the point marked 1,033 (ft) [315 m] on OS map (abundant)".

Variation

A recent study of Fermanagh O. secunda populations found there was very little genetic variation present in any of them. All the patches examined, including one with 140 ramets, proved monoclonal, ie they consist of a single genome. Reproduction involving extreme levels of clonal behaviour and a lack of flowering and fruiting probably represents a means of conserving energy in an unfavourable environment. The fragmented population stands of O. secunda in Fermanagh are near the southern margin of the species distribution in B & I, which is centred in the Scottish Highlands. As such these Irish stands represent relict populations left over from cooler periods in Earth's history. Thus range-edge effects, the availability of suitable habitat, plus grazing pressure from sheep and goats may well be factors determining the strong predominance of clonal growth observed. Under Irish temperate conditions, populations are found on exposed scarps, or less commonly in deciduous woodlands, rather than in the coniferous forests that represent the optimum boreal habitat of O. secunda. Thus what appears to be a sizeable population of Serrated Wintergreen may consist of only one or a very few genomes. Therefore the species lacks genetic diversity and is very much rarer than it looks (Beatty et al. 2008).

British and Irish occurrence

By far the greatest presence of O. secunda in B & I is in the Scottish Highlands and northern regions of Britain. Further south in Britain, and especially in Wales and Ireland, it appears to be a rare or very rare and declining relict species, although it is not clear if it has declined further since the 1970s (D.A. Ratcliffe, in: Stewart et al. 1994; F.J. Rumsey, in: Preston et al. 2002).

European and world occurrence

The overall distribution of O. secunda (taking the taxon in the wider sense, since Hultén (1971), Tutin et al. (1972) and Hultén & Fries (1986) recognise two subspecies), is a circumpolar boreal montane species, characteristic of and widespread within boreal forests and upland heaths around the N Hemisphere. It occurs throughout most of Europe and appears in a very much wider range of woodland communities than it does in B & I (Ellenberg 1988), but is rare in the Mediterranean region and quickly becomes scarce to rare south of the boreal zone and in lowland areas (Hultén 1971, Map 129; Hultén & Fries 1986, Map 1441). Serrated Wintergreen is widespread and frequent to abundant in subalpine heaths and coniferous woodlands at all levels throughout Switzerland where, indeed, it is the most widespread and frequently met member of the Pyrolaceae (Welten & Sutter 1982, 1, Map 1210).

Names

The genus name 'Orthilia' is of rather obscure origin, but the first part of the name comes from the Greek 'ortho' meaning 'straight' and probably refers to the female style. The Latin specific epithet 'secunda' in Classical language means, 'following', but in a botanical sense it means, 'arranged on one side only' (Gilbert-Carter 1964). The plant is too rare to have accumulated much in the way of English common names, apart from the obvious 'book names' or translations, for example, 'Secund Wintergreen' and 'Serrated Wintergreen'. The one exception is 'Yevering Bells' (Prior 1879), or 'Yavering Bells' (McClintock & Fitter 1956; Watts 2000), which the former helpfully explained is so called, "from a lofty conical mountain near Kirk Newton in Northumberland, where the plant was found growing wild". However, it turns out that all these gentlemen were mistaken, taking the geographical name of the site to be a local English common name. The correct name of the site is 'Yeavering Bell', the solitary station for the plant in VC 68, where it was discovered in 1834 and survives to the present day (Swan 1993).

Conservation status

Orthilia secunda is a protected species in Northern Ireland under Schedule 8 of the 1985 Wildlife Order by the Environment and Heritage Service.

Worth looking for additional sites

Since such a high proportion of Serrated Wintergreen plants exist in a purely vegetative state and they often hide underneath sub-shrubs such as Vaccinium spp., it is possible the species might yet be discovered in other suitably damp, reasonably undisturbed heathland sites elsewhere in the north of Ireland. It is likely that heath and heather moorland fires in the past have destroyed other populations throughout both B & I. Such losses have drastically restricted the distribution of this lovely little plant, which now, under the further threat of global climate change, really teeters on the brink of extinction in Ireland.

Threats

Forestry operations, including fire and fertilizer spraying.

MONOTROPACEAE – Bird's-nest family