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Pyrola media Sw., Intermediate Wintergreen

Account Summary

Native, very rare and probably facing extinction. Eurosiberian boreal-montane.

1904; Praeger, R.Ll.; on the shore of Lough Fadd.

Throughout the year.

Growth form and preferred habitats

Intermediate Wintergreen is a rare, rhizomatous, mycorrhizal, evergreen, perennial herb with a basal rosette of fleshy ovate or rounded leaves. While the plant produces a creeping underground rhizome that enables some degree of vegetative reproduction and clonal dispersal, this is a delicate organ of very slender dimensions, rather aptly described by the famous Victorian alpine explorer, gardener and plant collector Reginald Farrer as, "long, fibreless runners like fine macaroni, that never stops to rest" (Farrer 1930, 2, p. 203). P. media can produce a flowering scape up to 30 cm tall bearing a terminal raceme of 10-15 pendulous, white, globular flowers that are larger than those of P. minor (Common Wintergreen). However, it often fails to do so, the P. media plant rosettes remaining stubbornly vegetative.

The preferred growing conditions are semi-shaded, damp and mossy, yet well-drained, mildly acid to slightly basic, leached and nutrient-poor soils. On these types of substrate, it usually grows under the secondary canopy of ericaceous sub-shrubs on heaths (often upland) and in woods (especially pinewoods) (Stewart et al. 1994; Hill et al. 1999; F.J. Rumsey, in: Preston et al. 2002).

With regard to distinguishing the two Pyrola species that occur in Fermanagh (the other wintergreen present is now in the genus Orthilia), experience to date indicates P. media always occurs in very small populations of discrete leaf rosettes. It grows in crevices or ledges on sandstone cliff scarps, or under dwarf ericaceous sub-shrubs on the steep, overgrown talus slopes beneath these cliffs. This contrasts strongly with P. minor (Common Wintergreen) which occupies much more horizontal ground in light to medium density woodland shade, generally under a canopy of birch, rowan, ash and hazel. P. minor usually appears in considerable quantity, forming either discrete patches or wide carpets of growth and it flowers very much more freely than does either P. media or Orthilia secunda (Serrated Wintergreen).

Fermanagh occurrence

Praeger found this very rare species on the rocky shore of Lough Fadd on 3 July 1904, where it has not been seen since; he also recorded it among steep-sloping, sub-montane ericaceous heath on four or five north-facing dolomitized sandstone scarps (see below) in the Western Plateau, around what is now the Lough Navar Forest Park, on subsequent days in the same week (Praeger 1904). His separate sites, which he described as, "Shean North, 1,135 feet [340 m]" and, "Half a mile [0.8 km] south of Shean North", are very difficult to locate on old or modern Ordnance Survey maps and in a most unsatisfactory arrangement they are currently combined into an extant site for the species, the 'Radio Mast Scarp' at grid ref. H066572.

Despite this difficulty, the current author (RSF) and RHN are able to identify a total of seven stations for P. media in Fermanagh, four of them with post-1975 records. All seven are situated on the Western Plateau and they feature in a total of five tetrads, four with post-1975 records. Apart from the first record, all the sites are on the heathy scarps mentioned above or are associated with other named map features. The first five that follow are Praeger's sites from July 1904. The others were discovered by RHN & HJN on the dates given: scarp S of Carricknagower Lough (refound 2 November 1995); E end of Meenameen Lough; NE of Lough Anaban (refound 30 April 1995); at Shean North; half a mile [0.8 km] S of Shean North; scarp at Radio Mast, 7 August 1981 & 17 July 1982 (a solitary flower photographed); at Derryvahon Td, 500 m S of Sillees River, 9 March 1996, and monitored at the latter several times since.

The preferred ecological requirements of P. media of damp but drained, shaded, moderately acid, nutrient-poor conditions are very well met by the steep, heath-clad, north-facing, rock strewn slopes below the Lough Navar scarps, the rock of which is a weathered Old Red Sandstone in which mineral replacement has been effected by percolating lime-rich water seeping down from overlying Carboniferous strata.

Despite P. media possessing a slender, creeping rhizome, an organ enabling both energy storage and vegetative propagation, at its Fermanagh stations Intermediate Wintergreen is only present in extremely small plant numbers. As it grows beneath an evergreen heath canopy, P. media is made even more difficult to locate by the fact that many of the individual leaf rosettes are very small, often bearing only one or two leaves. Very rarely we have found individuals with up to ten fleshy evergreen leaves. At the four current Fermanagh stations we have never found more than 19 plant rosettes on any occasion and often only six or fewer small vegetative plants are present.

As in other areas of B & I, P. media is extremely shy when it comes to flowering in the Fermanagh sites' particular environmental conditions. We have seen the plant in flower only once (on 17 July 1982), when it was photographed. The infrequency of flowering in Fermanagh obviously severely curtails the production of the huge seed numbers essential to the success of the reproductive strategy of this species. We really must be observing a species declining towards inevitable local extinction.

Flowering reproduction

While flowering is extremely rare in the Fermanagh area at present, the flowering season of P. media is generally quoted as running from June to August, the leafless scape bearing between four and twelve pendulous white homogamous flowers. Pyrola flowers contain little or no nectar but are said to attract bees, flies and beetles which collect and feed on plentiful pollen (Proctor & Yeo 1973; Fitter 1987). In some species, including P. minor, the stigma produces a sticky fluid that insect visitors lick. Sell & Murrell (2014) state that nectar is secreted by the base of the petals in P. media. However, whatever the real situation is regarding an insect food reward, several important authorities on pollination agree that insect visits to Pyrolaceae are rare (Knuth 1903-1909; Hagerup 1954; Knudsen & Olesen 1993) and wind-pollination, or more likely, selfing, must be a common feature since the majority of flowers do form fruit capsules and set seed (Salisbury 1942; Hagerup 1954).

A detailed study of insect pollination ecology in Pyrolaceae carried out in Denmark and Sweden included three species of Pyrola, plus Orthilia secunda (Serrated Wintergreen) (which does produce nectar and scent) and Moneses uniflora (One-flowered Wintergreen) (Knudsen & Olesen 1993). These workers found that bumblebees were the principal visitors and although insect numbers were low in the habitat of these species, the fact that two or more species of Pyrolaceae often grow together may allow sharing of pollinators to the mutual benefit of the species. The anthers of Pyrola 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; they then harvest the pollen shower this process releases (Knudsen & Olesen 1993).

Seed and seedling ecology

All species in the Pyrola family possess very small, light seeds which are comparable to those of terrestrial orchids, but they have an even smaller central region containing the actual embryo (Salisbury 1942, p. 94). Members of the genera Pyrola and Orthilia may be regarded as semi-saprophytes, since although they possess evergreen leaves and are capable of photosynthesis, they require damp, humus-rich habitats and can endure deep shade. The diminutive food reserves of the seed, allied to a near-obligate relationship with a mycorrhizal fungal partner for germination as is common in most or all terrestrial orchids, reinforces the idea that the plants are probably best considered semi-saprophytic.

Measurements of fruit and seed production by Salisbury (1942) found that fruiting stems of P. media bore a range of between four and twelve capsules (mean 8.75), each containing an average of c 1,400 seeds. Salisbury calculated mean seed production lay between 10,000 and 14,000 per plant.

If flowering was a regular seasonal occurrence in the majority of leaf rosettes, then P. media could survive in the long term perfectly well, since the small seed allows very efficient dispersal and the mycorrhizal connection permits the tiny seed size without undue detriment to seedling establishment. It is obvious, however, that there is a smaller margin of safety against the risks of mortality in the earliest stages of development.

British and Irish occurrence

The New Atlas hectad map shows that in Britain P. media is very much more frequent in the highlands of E Scotland than elsewhere. The species has declined and all but disappeared from England and Wales. In Ireland, it has likewise declined to near extinction in the Republic (one recent record from Co Clare (H9), only) and it only appears to be maintaining itself in NI. Here, apart from Fermanagh, it is known from eleven hectad squares spread across three VCs (Cos Tyrone (H36), Antrim (H39) and Londonderry (H40)).

In view of the exceptionally shy flowering habit of P. media in our area, distinction of it from P. minor (Common Wintergreen) might appear difficult. Even when they do flower, the two species can appear similar enough to be confused. Locally in the FNEI 3 and more generally in the New Atlas, the editors recognise that these species have been mistaken for one another in the past. This makes it impossible to know for certain whether they are declining overall in the British Isles, although observers can be more certain of local changes in regularly visited sites (FNEI 3; F.J. Rumsey, in: Preston et al. 2002).

In Scotland and elsewhere in Britain, P. media is a rare member of the NVC H16 Calluna vulgaris-Arctostaphylos uva-ursi heath community. It is especially concentrated within and characteristic of a herb-rich version of this vegetation, the Pyrola-media-Lathyrus montanus sub-community (Rodwell et al. 1991b, p. 528). In Fermanagh, the heath vegetation where P. media occurs is much less herb-rich than Rodwell describes and in the total absence of Arctostaphylos the woody element is composed of some or all of Vaccinium myrtillus (Bilberry), V. vitis-idaea (Cowberry), Calluna vulgaris (Heather) (generally dominant) and Erica cinerea (Bell Heather). On the other hand, here in Fermanagh, Intermediate Wintergreen is regularly accompanied by its very rare relative (at least in an Irish context), Orthilia secunda (Serrated Wintergreen) and very occasionally by the rare and inconspicuous orchid Listera cordata (Lesser Twayblade). Nowhere in the GB-based NVC do we find P. media consorting with Orthilia secunda and we may probably take it that this particular rare form of Irish vegetation has yet to be investigated and described (Braun-Blanquet & Tuxen 1952; Ivimey-Cook & Proctor 1966; White & Doyle 1982). It may perhaps be a transitional stage from calcicole to calcifuge vegetation, due to prolonged leaching of the soil which is derived from a dolomitized sandstone.

European and world occurrence

In Europe, P. media is widespread in Northern boreal areas, extending S to the Maritime Alps and E to Continental Russia and boreal Asia. The locations for it in the British Isles form the western extremity of the core area of the species distribution and it is absent from immediately adjacent regions of the European continent including France (Hultén & Fries 1986, Map 1437).

Names

The name 'Pyrola' is the Latin diminutive of 'Pyrus', meaning or the name referring to the 'pear' tree and refers to the pear-like leaves of the species in the genus (Stearn 1992). The Latin specific epithet 'media' simply translates as 'intermediate', that is, a reference to the scale of this species between P. rotundifolia (Round-leaved Wintergreen) and P. minor (Common Wintergreen). The plant is too rare to have any English common names except the inevitable translated 'book name', 'Intermediate Wintergreen'.

The English common name 'Wintergreen' itself was first given by Turner (1548) in his The Names of Herbes, a straight translation of the German 'winter-grün', taken from the Ortus sanitatis or the Hortus sanitatis, also called the German Herbarius or perhaps best amongst further alternatives, just simply Cube's herbal, a medical text only partly reworked from earlier material by Dr Johann von Cube of Frankfort, dating from around 1485 or 6 (see Arber 1938, p. 22). Prior (1879) points out that in Danish 'winter-grönt' refers to the ivy, Hedera helix and he suggests that this is the rightful claimant of the name, being so conspicuously green when the majority of trees are bare of leaves.

The aromatic oil rub called 'Wintergreen' that is in everyday medicinal use by games’ coaches on the athletic field and which magically enables games’ players to get back on their feet, just moments after apparently life-threatening muscular sprain, was originally distilled from the low, creeping American ericaceous shrub, Gaultheria procumbens (Checkerberry). It has nothing whatever to do with the members of the Pyrolaceae. The original G. procumbens plant oil can cause severe skin eruptions and a synthetic replacement (methyl salicylate) is used nowadays to avoid the problem. Joking aside, Wintergreen really does relieve rheumatic, joint and muscle pains (Grieve 1931, p. 849).

Threats

Very few and very small, isolated populations vulnerable to any of type habitat change, especially those associated with forestry operations and heathland fires.