Silene vulgaris (Moench) Garcke, Bladder Campion

Account Summary

Growth form and preferred habitats

This is a very variable, long-lived, ± hairless, many-branched perennial arising from a stout, deeply penetrating taproot. At ground level, the plant produces a number of persistent, short, stout, woody stem bases from which erect or decumbent, flowering shoots are formed. Flowering stems up to 60 cm, bear oval, pointed leaves that vary greatly in length (up to 10 cm) and width, either broad or narrow (0.7-2.5 cm). In some strains, the leaves are slightly waxy or smooth, but others have leaves covered with short hairs (Salisbury 1964). The leaves are often blue-green (glaucous) in colour.

Bladder Campion is a lowland plant and weed of the margins of cultivated fields, gravelly hedge banks, roadsides, quarries and other occasionally or regularly disturbed, rough, grassy places. Although it occurs in a wide range of soils, it shows a preference for moderately fertile, open, calcareous, sandy or gravelly conditions with some humus present. It entirely avoids very wet, strongly acidic, peaty substrates.

S. vulgaris tolerates partial shade and can occur in woodland glades and edges, or on the banks of hedges and ditches (Sinker et al. 1985; Jonsell et al. 2001; P.S. Lusby, in: Preston et al. 2002). The range of disturbed wayside habitats indicates a definite anthropochorous link with man and his activities, which clearly assists seed dispersal and facilitates colonisation by creating suitable open habitat for the species.

Flowering reproduction

Flowering takes place from June to August. The flowers on any one plant of S. vulgaris are either unisexual (ie male or female) or perfect (ie hermaphrodite, male and female), but occasionally some may bear perfect and unisexual flowers. Male flowers are very rare, but have been reported in C Europe (Clapham et al. 1987). The flowers are produced on a branched cymose inflorescence, usually bearing around 30, rarely fewer than five, or up to 50 nodding flowers. The white flowers (rarely pink or greenish) have five free petals, with a tube around 10 mm deep; the limbs that spread at right angles at the calyx mouth are very deeply bi-lobed. The flowers are also very variable in their proportions, some bearing an urn-shaped, inflated sepal tube, while others have a more cylindrical, fused calyx. The number of styles is also variable, usually three, but there can be four or five on female and perfect bisexual flowers.

Pollination

The flowers produce fragrance and nectar at the base of the stamens only in the evening, and are principally pollinated by night-flying moths and flies. The anthers release their pollen at around 20.00 hours, and little remains the next morning. A large number of insect species are known to visit S. vulgaris flowers, including solitary bees, flies and moths. The long-tongued bees mop up any remaining nectar during daylight hours. Night-flying moths of the genus Hadena not only pollinate the flowers, but also lay their eggs in them, acting as 'parasitic pollinators' (Pettersson 1991).

Fruit and seed

The fruit capsule remains enclosed by the rather inflated calyx. The capsule is subglobose and becomes dry and somewhat leathery as it ages. When ripe, it splits at the top to form six (sometimes eight or ten) spreading teeth, and the seeds are shaken out by the wind. The kidney-shaped seeds, 1-1.6 mm, are greyish or black in colour (white when immature). They are covered with conical tubercles (projections, bumps) that vary considerably in height, ie low, rounded, high, acute, or even like flat plates, although the latter type is rare (Clapham et al. 1987; Jonsell et al. 2001; Stace 2010). Germination occurs in May and June, at least eleven months after seed production, and the germination success rate can be as high as 90%. The seed is also long-term persistent, a proportion surviving more than five years burial in the soil (Thompson et al. 1997).

Variation

It is absolutely clear from the content of the previous two sections, that S. vulgaris is an extremely variable species, varying considerably or even widely in almost every character one examines. There is a large body of evidence of this wide-ranging variation from two in-depth studies of S. vulgaris made by Marsden-Jones & Turrill (1957) and Aeschimann (1985). Bladder Campion varies, for instance, in leaf shape, hairiness and habit. It has been suggested that in Scandinavia this variation may be the result of repeated immigration from various geographical sources (Jonsell et al. 2001).

In Britain, hairy-leaved plants appear to be more prevalent on drier, more calcareous soils, suggesting a possible association with a physiological difference. However, in general in would seem that we have here an example of diverse genetic patterns, all of which have similar survival value, and thus different forms can persist side by side (Salisbury 1964, p. 186). In Scandinavia, on the other hand, local populations are often found to be homogenous with regard to seed wall sculpture (ie high or low tubercules), yet no correlation between seed form and ecology or geography has ever been discovered there (Jonsell et al. 2001).

In Flora Europaea 1 (2^nd edition), the variation in S. vulgaris is subdivided into five subspecies and the closely related maritime species, S. uniflora Roth, into a further four subspecies. Only two of the S. vulgaris subspecies occur in Britain, the widespread subsp. vulgaris, and the introduced and long established subsp. macrocarpa Turrill, which is tightly restricted to Plymouth Hoe in Devon (Stace 2010).

The variability within the S. vulgaris species aggregate is so great that in the past taxonomists have struggled to describe, delimit and classify the various subordinate entities. As many as four alternative genera have been proposed, for the taxon, namely Behen, Behenantha, Cucubalus and Oberna (Jalas & Suominen 1986, p. 55).

Fossil record and Status

Seed of S. vulgaris was "extraordinarily abundant in full Weichselian time where it was repeatedly found in geological conditions and faunistic evidence indicative of fresh soils, open habitats, salinity and severe periglacial climate" (Godwin 1975, p. 143). Seeds have also been found from the Wolstonian glacial stage. In contrast, there are no Flandrian fossil records at all (ie from the current warm interglacial period), except for those associated with Roman times, and from one Mediaeval site at Shrewsbury. The fossil evidence clearly indicates that S. vulgaris was well able to live through glacial stages, but almost certainly had much more difficulty contending with plant competition during interglacial woodland conditions (Godwin 1975).

When one considers the near absence of interglacial fossils for S. vulgaris, its absolute requirement for open habitats, and its definite link with sites created or strongly influenced by human activity (ie artificial and disturbed habitats), it is perfectly possible to conclude that Bladder Campion might well represent another archaeophyte to add to our growing list of ancient introduced species, now thoroughly naturalised in Britain and Ireland.

Fermanagh occurrence

S. vulgaris has always been a very rare species in Fermanagh. Robert Northridge and the current writer, RSF (the joint Botanical Society of Britain & Ireland Recorders for the county) have never seen it here, and there are just four records in the Fermanagh Flora Database. Additional to the first record listed above, the other three are: roadside at Cranbrooke near Fivemiletown, 1951, MCM & D; Clonmackan quarry, near the border and Clones, 1951, MCM & D; and Tattynuckle Td, near Fivemiletown, 1987-99, I. & D. McNeill.

Northern Ireland occurrence

Around Lough Neagh, Harron (1986) regarded S. vulgaris as, "very sparingly distributed, generally rare and a (non-persistent) colonist". In fact he listed just four records there, all of them Victorian! Similarly, the FNEI 3 lists a total of 45 records for the three counties, but only 13 of them are post-1970 and the majority (25 of them) are 19th century or earlier.

A careful examination RSF made of the 91 records for both S. vulgaris and S. vulgaris subsp. vulgaris in the N Ireland Vascular Plant Database covering all six counties in N Ireland, suggested that, despite an incomplete computerisation of early records and allowing for an increased recorder effort in recent decades, S. vulgaris remains scarce, but is not showing major decline in the other five VCs in NI.

British & Irish occurrence

Previously in Ireland, this was a more common and widespread perennial weed of cultivated fields, gravelly hedge banks and roadsides than is the case today (Mackay 1836; Cybele Hibernica 1866). In their day, Colgan & Scully (1898) suggested it was more frequent near the sea, but there probably was some confusion with S. uniflora Roth. (= S. maritima With.) (Sea Campion), although these authors did distinguish the latter.

S. vulgaris has always been much less frequent towards the N & W in both Britain & Ireland, disappearing completely or never recorded in much of Scotland and N & W Ireland. However, comparison of the two BSBI atlases shows there has been a rather surprising, appreciable decline since 1962 (BSBI Atlas 2; New Atlas).

A subsequent 'Local Change' re-survey in Britain of the 1987-8 'Monitoring Scheme' sample hectads and tetrads has shown that while S. vulgaris is not a strict calcicole, it is now frequent only on calcareous substrates. Furthermore, it appears that grassy field margins where it previously grew have now become too nutrient-enriched to provide the open vegetation structure the species requires, and plant competition has become too severe for it to survive there (Braithwaite et al. 2006).

The species is strikingly variable, both genetically and in response to environment. Plants are large and vigorous, dormant seed is long-persistent in soil, and when germination occurs, it enjoys a high level of success. Populations also occupy a wide range of disturbed and artificial habitats, so S. vulgaris is intimately associated with human activities. The observed gradual decline, and its very widespread extent, are therefore more than a little unexpected.

European and world occurrence: S. vulgaris is very widespread on the European continent, stretching in an almost continuous manner from the far north (70°N in Scandinavia), to the Mediterranean islands, and from the western coastline well into the eastern continental heartlands where it appears to gradually thin out (Jalas & Suominen 1986, Map 1109). According to Hultén & Fries (1987, Map 788) "This polymorphic, partly anthropochorous species is indigenous in Europe and large parts of Asia." The latter authors do acknowledge that S. vulgaris is widely spread by man into N & S America, S Australia, Tasmania, New Zealand and elsewhere. With its present distribution, the species (shown as S. cucubalus Wibel. in Hultén 1974, Map 214) belongs to the circumpolar plants.

Uses

Although we generally think of Bladder Campion as a weed of disturbed places, nevertheless in pastures in past times it was regarded as a good fodder plant. Young shoots, which appear in March or early April, were previously rated as a vegetable suitable for human consumption (Salisbury 1964). It is listed by Mabey (1972, p. 92) in his book Food for free, as a substitute for Chickweed (Stellaria media), itself now regarded as a substitute for Spinach.

Names

The origin of genus name 'Silene' is obscure (Gilbert-Carter 1964) but might possibly be derived from the Greek 'sialon' meaning 'saliva', referring to the gummy exude from the stem which wards off insects (Johnson & Smith 1946). Another suggestion is that 'Silene' is Theophrastus' name for another plant (Viscaria), a different Catchfly (Gledhill 1985; Stearn 1992). The Latin species epithet 'vulgaris' simply translates as 'common'.

There are a plethora of English common names, Grigson (1987) listing no less than 33 varied names, some more fanciful and unique than others. Quite a few names are shared with related species, particularly with Ragged-Robin (Lychnis flos-cuculi), Red Campion (Silene dioica) and White Campion (Silene latifolia). In addition to 'Bladder Campion', there are variants that include 'Bladder' such as 'Bladder bottle', 'Bladders of lard', 'Bladderweed' and 'Bletherweed'. Other names like 'Pop Guns', 'Poppers', 'Poppy', 'Corn pop', 'Snappers' and possibly 'Clapweed' and 'Cow-cracker', refer to the fact that the inflated calyx can be popped or snapped when young before the contained fruit capsule ripens. 'Rattle-bags', 'Rattleweed' and 'Cow-rattle', refer to the sound of the seed rattling in the shaken ripe capsule. 'Cow-rattle' might also suggest the calyx is shaped like a cowbell. The Scottish name 'Cowmack' refers to a suggestion or belief that the plant helped make the cow want the attentions of the bull. Six of the names Grigson lists refer to the white, night pollinated flowers, eg 'White Cockle', 'White Hood' and 'White Cock Robin' (Grigson 1987, p. 81-2).

Threats

Cultural eutrophication, caused by nitrogen and phosphate slurry and fertiliser drainage runoff from farmland, has increased the competition S. vulgaris faces from more vigorous plant species, leading to its displacement.

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