Portal de Periódicos da CAPES

Pinguicula L.

2004; Wiley; Volume: 92; Issue: 6 Linguagem: Inglês

10.1111/j.0022-0477.2004.00942.x

1365-2745

Y. Heslop-Harrison,

Plant Parasitism and Resistance

The genus Pinguicula L. (Lentibulariaceae, Butterworts) consists of some 50 species (Casper 1966) which are present on all continents except Australia and all but the extreme north-west of Africa. In Europe, 12 species were described by Casper (1972). Nine species (including two newly described by Blanca et al. 1999) occur on the Iberian peninsula, of which five are endemics. In the British Isles today there are just three species (i) P. vulgaris, (ii) P. grandiflora and (iii) P. lusitanica, and a fourth, P. alpina (iv), existed in Scotland at a very limited number of sites in the nineteenth century, and finally became extinct around 1900‡. In common with those in Spain, the representatives of the genus in the British Isles belong to the three subgenera into which it has been subdivided (Casper 1966), subgenus Pinguicula Casper for (i) and (ii), subgenus Isoloba Barnhart for (iii) and Micranthus Casper for (iv). The species are herbaceous, relatively short-lived perennials (although occasionally behaving as annuals) and of rosette habit whilst in active growth, some overwintering as hibernacula. Many reproduce vegetatively by means of bulbils and/or epiphyllous buds which later take root. Unlike members of the other two genera (Genlisea and Utricularia) in the family, all species of Pinguicula bear true roots, which are either fibrous, tufted, and often ephemeral, or, as in P. alpina, swollen and perennial. The leaves, which in most species lie appressed to the ground, are occasionally heterophyllous and the later formed ones may be larger and semi-erect (whereby the plant can tolerate more shaded conditions). The leaves are adapted for insectivory and bear glands of two types (stalked and sessile) on the upper surfaces. The stalked glands carry permanent mucilaginous droplets giving the characteristic greasy feel, and the generic name is derived from the Latin pinguis- fatty or greasy to the touch. The gland secretions can trap and digest prey, and the glands then absorb the products of digestion (Heslop-Harrison & Knox 1971; Heslop-Harrison 1978; Heslop-Harrison & Heslop-Harrison 1980, 1981), as first reported by Darwin (1875). Most species are confined to wet, relatively open sites and do not withstand much competition from other plants. Cladistic analyses have shown the ordinal classification of the family Lentibulariaceae to be placed accurately in the Lamiales (APG 1998), and the phylogenetic relationships of the genera Pinguicula, and Genlisea, inferred from rps16 and trnL-F sequence data, have been made in relation to molecular systematic studies (Jobson et al. 2003). Sequence analyses in most of the European species of Pinguicula have been made using the internal-transcribed (ITS) R DNA region by A. Schmidt (1998), and from these results he has proposed a phylogenetic tree for the species. The only DNA C-value recorded for the genus is for the American P. primuliflora, which was estimated to have a 1C DNA amount of 0.68 pg (= 669 Mbp) (Hanson et al. 2001). Common Butterwort. Subgenus Pinguicula, Section Pinguicula. An insectivorous perennial consisting in summer of a rosette of 4–7(−11) leaves lying close to the ground, shallowly anchored by a tuft of fine, fibrous roots. Overwintering as a hibernaculum. Leaves sessile, bright, yellowish-green ('pod green', 61/1 of British Colour Chart 1941), occasionally pink-tinged on lower surface, somewhat fleshy in texture, the upper surface bearing stalked glands holding secretion droplets giving the characteristic greasy feel. Laminae (1.0–) 2.5–5.0(−9.0) cm long (0.07–)1.0–2.0(−2.7) cm wide, ovate-oblong, increasing in size towards the end of the growing season; margins entire and capable of inrolling after stimulation of the upper surface by an insect or other nitrogenous material. Scapes ebracteate, 1–8 per plant, produced in succession in early summer; one, rarely two, per leaf axil, yellowish-green or tinged with purple, glandular (5–)6–15(−27) cm long, increasing in length as the fruit develops. Flowers solitary, bisexual and zygomorphic. Normally the flower assumes a horizontal posture at anthesis, but is occasionally held more or less erect. Calyx greenish-purple, glandular externally, bilabiate, the upper lip 3-lobed, with the lobes dissected to the middle or less; lower lip 2-lobed, the lobes ovate or oblong, acute or subacute and split to 2/3 of the calyx length. Corolla lilac or blue-violet (735/1 or 39/1 of British Colour Chart), with darker markings of violet (36/1), 14–20 mm in total length (tip of lower lip to end of spur), with the anterior portion bilabiate and expanding into 5 oblong, flat lobes, 2 above and 3 below; lower corolla lip 0.7–1.2 cm wide, without a palate, the almost rectangular lobes not overlapping and without the wavy margins characteristic of P. grandiflora. Honey guide in the form of an indistinct white or paler area on the lower lobe, bearing numerous uniseriate, multicellular hairs guarding the entrance to the corolla tube, the hairs also extending beyond the paler area for c. 1/2–1/3 the length of the lower lip. Corolla tube whitish internally, with indistinct brown-purple lines running into the spur. Posterior portion of the corolla tube extending backwards from between the sinus of the lower calyx lip, contracted into a straight or slightly downwardly curved, conical spur, 2–5(−10) mm long, the tip rarely bifid. The 2 stamens inserted opposite the 2 anterior sepals, the white or pale purple filaments curving round the ovary until the 2 patelliform anthers lie side by side, just below the stigmatic flap. Pollen grains spherical, stephanocolporate with 6–8 pores and a finely reticulate sexine, 33–36 µm in diameter. Stigma sessile, reduced to 2 flaps, the upper usually tiny, the lower larger and pendulous, with fringed margins, wet surfaced at maturity, and normally hanging in front of the anthers. Carpels 2, forming a unilocular ovary giving rise to an ovoid or spindle-shaped capsule, 0.5–1.0 cm long and 0.3–0.5 cm wide. Developing fruit at first horizontal, becoming erect at maturity and dehiscing along the placental margins. Ovules anatropous with a single integument, the seeds developing on a free-central, kidney-shaped placenta. Seeds small and powdery, ellipsoidal, 0.5–0.9 mm long, 0.16–0.32 mm wide with a reticulate, brown testa, the alveolar reticulations rather elongated; non-endospermous. Mean seed mass (air-dried) 23.8 µg (from sample from subarctic Sweden, ex Karlsson 1986). Embryo straight. Seedlings with a single cotyledon. Rather uniform in Britain in the wild, but possibly more variable in size, form and colour elsewhere in Europe, Asia and North America. The var. bicolor Nordstr. ex Fries has been recorded from Lough Derg, Ireland (Bot. Irl. 1934, p. 354) and Scandinavia (Casper 1962). Pinguicula bicolor Wol. (Zurzycki 1954) has the calyx members more deeply incised, white corolla lobes and purple spur; plants with these features have also been found in some British populations, but the form is best regarded as a variant of P. vulgaris, not a distinct species (Casper 1962). A variety with white flowers was found in Morven, Caithness (Dickie 1860), possibly the equivalent of the continental f. albida (Behm.) Neumann. Another form with the lobes of the lower lip of the corolla contiguous was recorded in Britain (Newbould ex Sowerby Engl. Botany 1863, p. 123) and also in Sweden (Casper 1962; quoting Melander 1883, and Neumann 1901). A form with deformed spurs has been reported in east Ross-shire (Duncan 1980). Many morphological variants have been observed during the cultivation of large numbers of plants of this species; these involved the absence, fusion or bifurcation of one or more of the calyx or corolla lobes, and occasional petaloidy of the calyx or stamens (Y. Heslop-Harrison, unpublished); the extent of white colouration at the entrance to the corolla tube also appeared to vary considerably. Native. This insectivorous perennial occurs mainly in seepage channels in the less acid parts of bogs, mires, calcareous fens and flushes, wet heaths and on wet rocks. Pinguicula vulgaris is a northern, disjunctly circumpolar species, and belongs to the Circumpolar Boreal-montane element (Preston & Hill 1997). It is common in the northern and upland parts of the British Isles, but becomes much more local in south Ireland; in lowland and southern parts of England it is absent from large areas (Fig. 1). In East Anglia there is a marked reduction in the Norfolk sites since 1962; its scarcity has been probably accentuated recently by the drainage of suitable habitats for agricultural and other purposes. The species is widespread in Europe, extending into Corsica, Italy and Macedonia and across Siberia into north Asia (Casper 1970) but it thins out eastwards to western Ukraine (Fig. 2). Its most northerly limit is on the east coast of Greenland (73°11′ N) and it occurs in Iceland, throughout Scandinavia (Hultén 1950), and southwards into central Spain and north Portugal. Its occurrence in north Morocco is reported by Blanca et al. (1999), but some earlier reports were said to be based on misidentifications (Romo et al. 1996). In North America it extends from Alaska in the north, throughout Canada from Newfoundland to British Columbia, and as far south in the USA as northern New York State (Fernald in Gray's Manual, edn 8, 1950; Hitchcock et al. 1959), the southern limit being roughly equivalent to that in Europe. In China, Japan and the western coastline of North America it seems to be replaced by P. macroceras Link, distinguishable from P. vulgaris by the larger calyx, with the lobes of the lower lip separated for half of their length, the larger corolla with deeply rounded lobes to the corolla lip, and the longer spur (Casper 1962). The northern and eastern limits of P. macroceras in the USA, however, are incompletely known (Fig. 2), and Hultén (1948) was unsure that this species could always be regarded as distinct from P. vulgaris. The distribution of Pinguicula vulgaris in the British Isles. (○) Pre-1950; (•) 1950 onwards. Each symbol represents at least one record in a 10-km square of the National Grid. Mapped by Henry Arnold, Biological Records Centre, Centre for Ecology and Hydrology, using the DMAP programme. Records mainly collected by members of the Botanical Society of the British Isles. The distribution of Pinguicula vulgaris world-wide; its main area of distribution lies within the shaded areas within the continuous line, and the triangles show its scarcer presence within the dotted lines. The distribution of the related P. macroceras in Asia and North America is also shown (see text); its presence is shown as circles within dot/dashed areas. Adapted by Glyn Woods, from Casper (1962) and Hultén (1950, 1958). Of the representatives of the genus in the British Isles, P. vulgaris has the greatest altitudinal range for it grows luxuriantly close to sea level on the west coast of Scotland and in Ireland; in Wales and northern England it is quite common above 300 m (even 'abundant', Bevis & Jeffery 1911) and in Scotland it occurs up to c. 1040 m (Fl. Br. Isl.); in west Mayo it occurs over 600 m (Praeger 1909, 1930, 1950). Elsewhere in Europe it grows most commonly in subalpine stations from 600 m to 850 m but ascends to c. 2600 m in the Pyrenees (Blanca et al. 1999), c. 2200 m in the Alps and up to 910 m in Norway (Casper 1962). Geographical and altitudinal tolerance of the species is correlated with the seasonal variations in temperature that it can withstand, and the duration of the growing season; altitude does not appear to limit its distribution in the British Isles (see also II). A high humidity requirement during the growing season limits the number of suitable habitats available (by means of a high water table, a constant water supply, snow melt and rainfall, etc.) for the species, and it can survive only some degree of desiccation as a hibernaculum. In Britain its distribution seems limited by the number of suitable wet areas available, whether sloping or flat; also presumably wherever the precipitation/evaporation (P/E) ratio (effectively humidity) is high enough for it to grow. Thus it can be found colonizing slopes of as much as 30° on hillsides facing the sea with a sandy substratum in the west of Scotland. It also grows occasionally in very slowly moving shallow water that neither immerses the leaves nor dislodges the shallow root system. On hills in Sutherland it was found predominantly on north-facing slopes (Gimingham & Cormack 1964), perhaps because the south-facing areas became too dry during periods of summer sunshine. This northerly preference confirms an early record of its occurrence only on the north-west side of the Malvern hills (Worcestershire), but not on the south or south-eastern slopes (Ballard, ex Withering 1818). Although primarily distributed in the north-west of Scotland, Wales, Ireland and the western parts of England where the average rainfall may be c. 800–1200 mm per annum, it also occurs in a runnel flora in the fens in East Anglia, where it is part of the Schoenus nigricans–Juncus subnodulosus mire community (Rodwell 1991b). Pinguicula vulgaris can withstand freezing as a hibernaculum, but not during the growing season, and the duration of this will control its altitudinal limits throughout its range. The hibernaculum can withstand several centimetres of snow cover for some months. In subarctic Sweden it is most commonly found in stabilized frost polygons, whereas P. alpina occurs in more active polygons (Karlsson 1986; Svensson et al. 1993; Eckstein & Karlsson 2001), but the two species may occasionally grow together in 'wet holes' amongst polygons (Mendez & Karlsson 1999). The occurrence of P. vulgaris in any particular locality seems to be governed mainly by the availability of water rather than by the type of substratum. Although shallow rooting, it can colonize wet rock faces as well as peaty or sandy ground kept permanently moist by seepage. The minimum and maximum soil pH ranges of the communities in which P. vulgaris occurs are in the Calluna vulgaris–Eriophorum vaginatum blanket mire (M19) at 3.1–6.2 and the Carex dioica–Pinguicula vulgaris mire (M10) at 5.8–7.2 (Rodwell 1991b). In western Scotland, where P. vulgaris occurred on calcareous peat or marl in a Schoenus nigricans mire, a pH of 8.0 was recorded (Veg. Scot., p. 439). In the Schoenus nigricans–Juncus subnodulosus mires (M13) of East Anglia and Anglesey (Rodwell 1991b) the flushing waters had a pH of between 6.5 and 8.0, with dissolved calcium levels of 60–200 mg L−1 (Wheeler 1975, 1984). In Ireland, apart from its more typical habitat, it occurs along the shores of the calcareous lakes of Lough Derg, Co. Donegal, and Loughs Corrib and Carra, Co. Galway (Bot. Irl.). Praeger describes the waters of the latter as a 'wonderful pale pellucid green … (being derived mainly from springs) … partly due to a curious soft, whitish calcareous deposit which envelops the whole bottom of the lough and reflects the light'. Values of soil and water pH for P. vulgaris in British fens are given in Table 1, and at three sites in northern Sweden, together with soil water and ash content. Within the United Kingdom it 'seems to show pronounced regional variation in the range of base-richness it regularly accommodates' (B.D. Wheeler, personal communication), and its occurrence does not always relate to the type of habitat available in any area. Thus 'in East Anglia, to the best of my knowledge, it is invariably associated with highly calcareous mires, though lower pH mires, whilst rather scarce in the area, do occur'. Wheeler also notes that 'in the New Forest area P. vulgaris is absent from base-rich sites which are well within its normal range elsewhere in lowland England, as well as being absent from the base-poor mires that are also within its range elsewhere in the UK (but not in southern or eastern England)'. He also wonders 'why does P. vulgaris not grow in many of the base-poor sites favoured by P. lusitanica, as these are undoubtedly within its ecological range' (this is discussed further in the account of the latter species). In 1911, in east Leicestershire, P. vulgaris grew 'in a limestone swamp' and was 'rediscovered' there in 1933 on leached-out detritus and peat on limestone (Horwood & Gainsborough 1933). Elsewhere in Europe P. vulgaris is 'indifferent to soil type' (Blanca et al. 1999). As in the British Isles it has a wide pH tolerance from Scirpus cespitosus associations, pH 4.9 (Böcher 1954), to pH 5.7–7.2 in others in the west Pyrenees (Turmel ex Casper 1962). In Swedish Lapland, in a subalpine tundra at Abisko (68°21′ N, 18°49′ E), the soil pH surrounding plants of P. vulgaris was 5.6 ± 0.2, but at Katterjakk, 24 km west of Abisko, it was 4.1 ± 0.1 (Aldenius et al. 1983). In the Norwegian arctic it occurs occasionally in areas inundated by the sea (Norman 1894–1901). According to Molau (1993), who studied the species in west Greenland, and at sites in the Abisko mountains and at Latnjajaure Field Station, Sweden, it was found in base-rich habitats. Braun-Blanquet (quoted by Bauquis & Mirimanoff 1970) believed that P. vulgaris was usually asssociated only with areas rich in calcium and that, if the species occurred on gneiss, it was because there was a supplementary source of calcium. Favarger (1962) proposed the testing of this theory by analysing the calcium content of water running off gneiss in Val d'Emaney, Haute Savoie, France. However, Bauquis & Mirimanoff (1970) analysed the seepage water from this, as well as from other localities where the substratum was of calcareous origin (and where the species was abundant) and concluded that calcium was not a factor governing the distribution of P. vulgaris; the amounts of calcium in ground water varied from 7.15 to 164.0 mg L−1. That P. vulgaris is absent from certain areas of Scandinavia and Germany, as well as parts of North America well within its range, suggests that some of its requirements, or tolerances, are not, as yet, understood. Ratcliffe (1964a Veg. Scot., p. 433) draws attention to the fact that some species have different nutrient tolerances in different parts of their geographical range 'with the general tendency to become more exacting and calcicolous towards their limits'. In the eastern United States the species is chiefly limited to calcareous soils (Fernald 1950, p. 1308). In the British Isles Pinguicula vulgaris is most characteristic of marshes, mires and wet, peaty heaths and fens. In these habitats it is restricted to areas where the associated plants are relatively low growing for, being a rosette plant appressed to the ground, it cannot tolerate much shade from taller vegetation. Wherever sites have been subjected to drainage in the past it is usually lost to the community. Its comparative rarity in the East Anglian Fens has been explained by the excessive height of this community of plants, as well as drainage of the area (Gilmour & Walters 1954); whilst in Dorset its disappearance was explained by possible climatic amelioration in recent times (Good 1953, p. 257). It never grows directly amongst Sphagnum, perhaps because it cannot compete here with the upward growth of this plant, so it tends to be associated rather with the wetter seepage channels. In Scotland, it is often found in open stony flushes with a very sparse plant cover (often of less than 50%), which, nevertheless, consists of a very distinct assemblage of plants, the most abundant species, apart from P. vulgaris, being Carex demissa (C. viridula ssp. oedocarpa), C. panicea, Festuca ovina agg., Juncus triglumis, Saxifraga aizoides, Thalictrum alpinum and Blindia acuta– such assemblages being found in open places between birch-juniper woods (Veg. Scot.). In the west of Scotland it is also found as a member of wet areas of the machair community, but this habitat is rather atypical for it. On the Isle of Skye it was recorded in a rich upland fen as a constant in the Eriophorum latifolium–Carex hostiana association along with Carex viridula ssp. oedocarpa, C. panicea, Drosera anglica. Eleocharis quinqueflora, Eriophorum latifolium, Schoenus nigricans, Campylium stellatum and Scorpidium scorpioides (Birks 1973). The British National Vegetation Classification (NVC) (Rodwell 1991b, 1992) records P. vulgaris in a range of mire, blanket mire, springs, flushes, wet heath and heath, and calcicolous and calcifugous grassland communities as well as on wet rock ledges, exposed rocks and cliffs. Pinguicula vulgaris is a constant, with a frequency of 81–100% occurrence in the samples examined in the Carex dioica-Pinguicula vulgaris mire (M10) as a whole and in several of its subcommunities and variants (Table 2). These are of widespread, but local, occurrence in northern England and Scotland, on soligenous mineral soils and shallow surface peats kept wet by base-rich, calcareous and oligotrophic waters. It is also constant in the Cratoneuron commutatum–Eleocharis quinqueflora subcommunity of the Carex viridula ssp. oedocarpa–Saxifraga aizoides mire (M11) which occurs in the Scottish Highlands, Southern Uplands, the Lake District, the northern Pennines and in north Wales. Other mire communities in which P. vulgaris occurs with a frequency of 61–80% in the samples studied are: the Carex hostiana–Ctenidium molluscum variant of the subcommunity (M10a), which is confined mainly to northern England and Scotland; and the Briza media–Primula farinosa subcommunity (M10b) and its flush vegetation variant Molinia caerulea–Eriophorum latifolium. In the latter variant, from Tarn Moor in Cumbria, and Upper Teesdale, the hummocks produced by the trampling of grazing animals provide excellent habitats for P. vulgaris rosettes. In the third subcommunity of M10, Gymnostomum recurvirostrum (which is confined to Upper Teesdale) hummocks are produced by the breakdown of this moss by wind erosion and age. The sheltered lee sides of the hummocks, amongst the gravel flushes, then provide sites for P. vulgaris and other rosette-forming dicotyledons. Pinguicula vulgaris is also a constant, but with the lower frequency, in the Carex viridula ssp. oedocarpa–Saxifraga aizoides (M11) community of open, stony flushes irrigated by relatively moderate base-rich waters on slopes in the montane to submontane parts of Britain; it is also present in the Thalictrum alpinum–Juncus triglumis subcommunity, which is confined to higher altitudes. It occurs likewise in the Polygonum viviparum variant (limited to the Clova-Caenlochan area) of this subcommunity and in the Juncus bulbosus/kochii–Saxifraga stellaris variant. Other communities in which it has the same constancy are the Briza media–Pinguicula vulgaris subcommunity of the Schoenus nigricans–Juncus subnodulosus mire (M13), which is restricted to Anglesey and East Anglia, and the Carex panicea subcommunity of the Scirpus cespitosus (Trichophorum cespitosum)–Erica tetralix wet heath (M15). This latter occurs mainly as small stands in soakways or water tracks in the wetter western and northern parts of Britain. Pinguicula vulgaris occurs with the same frequency in the Saxifraga aizoides–Alchemilla glabra banks community (U15), which is restricted to calcareous cliff faces in the Scottish Highlands and, occasionally, the Lake District. Pinguicula vulgaris is also frequent (III, 41–60%) in the following communities (Rodwell 1991b, 1992): the Briza media–Primula farinosa subcommuniy of the Carex dioica–Pinguicula vulgaris community (M10), Thymus polytrichus–Racomitrium uliginosum variant, centred in Upper Teesdale, with Plantago maritima and Thalictrum alpinum occasional; the Carex saxatilis mire (M12) which occupies high-montane flushes irrigated with base-rich and calcareous waters in Scotland; the mainly upland Saxifraga aizoides–Ditrichum flexicaule subcommunity of the Festuca ovina–Agrostis capillaris–Thymus polytrichus grassland community (CG10c); and in the Dryas octopetala–Silene acaulis ledge community (CG14) on ungrazed ledges and crags of calcareous bedrock at 300–900 m, mainly in the central and southern Highlands of Scotland. At frequency II (21–40%), P. vulgaris occurs in various other open fen and flush communities (Rodwell 1991b, 1992): the Carex rostrata–Calliergon cuspidatum/giganteum mire (M9) in north-west Britain and (frequency I) Anglesey; the Schoenus nigricans–Juncus subnodulosus mire (M13), widespread but local in England and Wales; the montane Anthelia julacea–Sphagnum auriculatum spring community (M31) where the ground in north-west Britain is kept wet by the trickling oligotrophic water (pH 4.5–5.0); the Calluna vulgaris–Arctostaphylos alpinus heath community (H17a) in the north-west Highlands of Scotland; the Sesleria albicans–Galium sterneri grassland community (CG9c) on calcareous soils in the northern Pennines; the Festuca ovina–Agrostis capillaris–Alchemilla alpina grass heath community (CG11b) in Scotland and Cumbria; the Dryas octopetala–Carex flacca heath (CG13a) in calcareous flushes in north-west Scotland; and the Luzula sylvatica–Geum rivale tall-herb community (U17a) on ungrazed calcareous mountain ledges in north-west Britain. In many NVC communities (Rodwell 1991b, 1992), P. vulgaris is scarce (I) including: the Carex rostrata–Sphagnum warnstorfii mire (M8), on raw peat with calcareous drainage, in the central Highlands of Scotland; base-rich seepages within the Trichophorum cespitosum–Erica tetralix wet heath (M15) in the wetter western and northern parts of Britain; Philonotis fontana–Saxifraga stellaris spring (M32) in the Scottish Highlands, Lake District, Pennines and Northern Wales; Carex viridula ssp. oedocarpa–Koenigia islandica flush (M34) on Skye only, with seepage water from springs of pH c. 6.0; Cratoneuron commutatum–Festuca rubra spring (M37), with seepage from lime-rich bedrock, in the north-western uplands of Britain and Calluna vulgaris–Arctostaphylos alpinus heath (H17) in Scotland and Orkney. Other notable communities supporting P. vulgaris in Britain are given in Table 3. The Ecological Flora of the British Isles (Fitter & Peat 1994) lists the following Corine habitats (Corine codes in brackets) for P. vulgaris: Atlantic cliff communities (C18.21), northern wet heaths (C31.11), Boreo-alpine Scottish heaths (C31.45), mountain avens mats (C31.49), British roseroot community (C31.64), sub-Atlantic semi-dry calcareous grasslands (C34.32), Agrostis–Festuca grasslands (C35.12), lowland blanket bogs (C52.1), upland blanket bogs (C52.2), soft-water springs (54.11), hard-water springs (C54.12), black bog-rush fens (C54.21), brown bog-rush fens (C54.22), dioecious-flea-yellow sedge fens (C54.25), arcto-alpine riverine swards (C54.3), acidic fens (C54.4), transition mires (C54.5) and inland cliffs and exposed rocks (C62). In the typical mire (M10) of Rodwell (1991b), and its Schoenus nigricans variant, P. vulgaris occurs with a frequency of 81–100%, P. lusitanica is also present, but with smaller frequency (Table 2). However, P. vulgaris often occurs independently of this species. Similarly, P. lusitanica may grow in communities independent of P. vulgaris, indicating their ecological differences. For the association of P. vulgaris with P. alpina see Section II(A); and for its association with P. grandiflora see the account of that species. In Central Europe, Ellenberg (1988) lists P. vulgaris as a character species of the Order Tofieldietalia (calcareous small sedge fens) and characterizes it as a light-loving plant of moderately wet, weakly acid to weakly basic, nitrogen-poor soils; Oberdorfer (Pfl. Exk.) noted its occurrence in mostly base-rich spring communities. In the Netherlands, Schaminee et al. (1995) have it in the Parvocaricetea, small sedge-fens, notably the Campylio–Caricetum dioicae, and also in species-rich examples of wet heath. Further north, in the Rondane, in south Norway, Dahl (1956) recorded it on hard acid rocks in only two communities, the Drepanocladeetum revolventis (constancy II) at 1100–1170 m. In central Sweden, in the mire complex at Skatiosberg Stormosse, Sjörs (1948) reported P. vulgaris with high constancy only in the Schoenus ferrugineus–Tomenthypnum–Campylium stellatum–intermedius association in a limited area which had a high calcium level (18 mg L−1; pH 7.1); he also noted it, but rarely, in the spring community, the Geum rivale–Philonotus fontana–Drepanocladus purpurascens association. In northern Sweden, the dominant species, where P. vulgaris occurs, are Arctostaphylos alpina, Betula nana, Empetrum nigrum ssp. hermaphroditum, Loiseleuria procumbens and Cladonia spp. (Karlsson et al. 1987); other associated species in this area are Eriophorum vaginatum, Rhododendron lapponicum, Tofieldia pusilla, Vaccinium spp. and carpets of Sphagnum spp. (Karlsson 1986, 1988). In west-central Iceland, species listed most constantly associated with P. vulgaris in damp, dwarf-shrub heath included Empetrum hermaphroditum and Betula nana. In nearby areas, P. vulgaris was in heath associated with Vaccinium uliginosum, Empetrum hermaphroditum, Salix herbacea, S. lanata, Bistorta vivipara, Thalictrum alpinum, Bartsia alpina and Carex bigelowii (Proctor 1972). In Greenland P. vulgaris grows in gravelly tracts associated with Betula nana and Loiseleuria procumbens (Heide 1912). Pinguicula vulgaris is shallow rooting and the rosette leaves are both delicate and brittle, and as such it does not survive either direct trampling or grazing by large herbivores such as sheep, cattle, ponies and various species of deer, during the growing season. However, the areas where it grows are usually unenclosed, and the trampling effect of such stock may contribute towards keeping the communities rich and open, and the more vigorous and taller species in check. Poaching may even be beneficial in the long term, by providing regen