<i>Pinguicula</i> L.

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 the soil pH plants of P. vulgaris was but at west of it was et al. In the it occurs occasionally in areas by the sea to the species in west and at sites in the and at Sweden, it was found in base-rich by & 1970) that P. vulgaris was usually only with areas in calcium and the species occurred on it was because there was a of (1962) proposed the of this by the calcium of water running in & the seepage water from as well as from other where the substratum was of calcareous where the species was and that calcium was not a the distribution of P. the of calcium in ground water from to mg P. vulgaris is absent from areas of Scandinavia and as well as parts of North America well within its that some of its or are as Scot., p. to the that some species have in parts of their range the to more and towards their In the eastern United the species is limited to calcareous (Fernald p. In the British Isles Pinguicula vulgaris is most characteristic of mires and wet, peaty heaths and In these habitats it is to areas where the associated plants are relatively growing being a rosette plant appressed to the ground, it tolerate much from sites have been to drainage in the it is usually to the Its in the East has been by the of this community of as well as drainage of the area & whilst in its was by in p. It grows amongst perhaps because it with the of this plant, it to be associated rather with the seepage In Scotland, it is often found in open with a very plant cover of less than consists of a very distinct of the most species, apart from P. vulgaris, being Carex and being found in open between (Veg. In the west of Scotland it is also found as a of wet areas of the but this habitat is rather for On the of it was recorded in a upland as a constant in the along with Carex Schoenus and The British National (Rodwell P. vulgaris in a range of mire, blanket mire, flushes, wet and and and communities as well as on wet rock and Pinguicula vulgaris is a with a of occurrence in the in the Carex vulgaris mire (M10) as a whole and in several of its and variants 2). are of but occurrence in northern England and Scotland, on and shallow surface kept wet by calcareous and It is also constant in the of the Carex mire which occurs in the the the northern and in north mire communities in which P. vulgaris occurs with a of in the the Carex variant of the which is confined mainly to northern England and and the and its variant In the latter from in and the produced by the of habitats for P. vulgaris In the of is confined to are produced by the of this by and The of the amongst the flushes, then sites for P. vulgaris and other Pinguicula vulgaris is also a but with the lower in the Carex community of by relatively base-rich waters on slopes in the to parts of it is also present in the which is confined to It occurs in the variant to the of this and in the communities in which it has the are the vulgaris of the Schoenus nigricans–Juncus subnodulosus mire which is to Anglesey and East Anglia, and the Carex of the Scirpus cespitosus wet This latter occurs mainly as small in or water in the western and northern parts of Pinguicula vulgaris occurs with the in the community which is to calcareous faces in the the Pinguicula vulgaris is also in the communities (Rodwell the of the Carex dioica–Pinguicula vulgaris community in with and the Carex mire which with base-rich and calcareous waters in the mainly upland of the community and in the community on and of calcareous at mainly in the central and southern of Scotland. P. vulgaris occurs in other open and communities (Rodwell the Carex mire in north-west Britain and the Schoenus nigricans–Juncus subnodulosus mire widespread but local in England and the community where the ground in north-west Britain is kept wet by the water the Calluna community in the north-west of the community on calcareous in the northern the alpina community in Scotland and the in calcareous in north-west and the community on calcareous in north-west In many communities (Rodwell P. vulgaris is scarce the Carex mire on peat with calcareous in the central of base-rich within the wet in the western and northern parts of in the and Carex on with seepage water from of pH c. with seepage from in the of Britain and Calluna in Scotland and communities P. vulgaris in Britain are given in Table The of the British Isles & the habitats in for P. communities northern wet heaths heaths British community calcareous lowland blanket upland blanket fens brown fens fens fens mires and and In the typical mire (M10) of and its Schoenus nigricans P. vulgaris occurs with a of P. is also but with 2). P. vulgaris often occurs of this species. P. may grow in communities of P. vulgaris, their ecological the of P. vulgaris with P. alpina Section and for its with P. grandiflora the account of that species. In Europe, P. vulgaris as a species of the small and it as a plant of wet, acid to its occurrence in base-rich In the et al. have it in the small the and also in of wet north, in the in south recorded it on acid in only two the at In central Sweden, in the mire at (1948) reported P. vulgaris with high only in the Schoenus in a limited area which had a high calcium level mg pH he also but in the the In northern Sweden, the species, where P. vulgaris are alpina, and (Karlsson et al. other associated species in this area are and of (Karlsson In Iceland, species most associated with P. vulgaris in and In P. vulgaris was in associated with alpina and Carex In Greenland P. vulgaris grows in associated with and Pinguicula vulgaris is shallow and the rosette leaves are and and as it does not survive either or by large as and species of during the growing the areas where it grows are usually and the of may towards the communities and and the more and species in may be in the long by

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