Calystegia silvatica (Kit.) Griseb., Large Bindweed

Account Summary

Growth form and preferred habitats

C. silvatica is a rather glamorous, very large white-flowered bindweed, originating from the Mediterranean region and SW Asia. It differs from both subspecies of its close relative C. sepium in that the two large bracteoles at the base of the flower overlap one another and completely conceal the calyx. It was not until the 1930s that the two species were separated in the field (Praeger 1934; Lousley 1948; Stace 1961), but it is now recognised that C. silvatica is a garden introduction to B & I from S Europe, which probably arrived in Britain sometime in the early 19th century, admired as a cultivated decorative flowering plant.

An illustration of C. silvatica produced in 1777 suggests it was in Great Britain by that early date (Salisbury 1964, p. 292). However, another more or less contemporary commentator, John Claudius Loudon (1783-1843), the founder and 'conductor' of The Gardener's Magazine and The Magazine of Natural History, suggested C. silvatica was first introduced to British gardens as late as 1815 (Loudon 1830; Walters & Webb 1956). Some authorities feel it was not reliably recorded in Britain until 1867, the date of a BM herbarium specimen (Ellis 1993). However, the 1867 specimen in the BM from Twickenham Park (VC 21), regarded by Lousley (1948) as C. silvatica, was later re-examined by Brummitt & Heywood (1960) and pronounced by them, "a poor specimen, ... almost certainly C. pulchra". Herbarium specimens collected from the wild in Britain have now been reported dating from 1863 (Stace & Crawley 2015).

Whatever date Large Bindweed was first introduced to B & I as a decorative garden subject, it subsequently escaped 'over the wall' into the wild, and was already growing widespread in lowland Britain and the more populated parts of Ireland when Lousley was writing of it in 1948. One wonders just how long it took gardeners to realise that they had a pernicious weed on their hands, and exactly when did they begin discarding it on waste ground, old quarries and the like?

C. silvatica is a plant of drier habitat conditions than C. sepium (Hedge Bindweed) avoiding the marsh and fen situations so characteristic of the latter (Garrard & Streeter 1983). It occurs most commonly near habitation in gardens, on fences, in hedgerows and on waste ground including in old quarries (An Irish Flora 1996). It can occasionally also colonise semi-natural habitats further from habitation, presumably spread by seed, although vegetative fragments of root and rhizome can also travel in mud, eg attached to vehicle tyres (G.M. Kay, in: Preston et al. 2002). Like C. sepium, with which it shares many ecological characteristics, the established strategy of C. silvatica is categorised as intermediate between Competitor and Competitive Ruderal (C/CR) (Grime et al. 1988, 2007).

Variation

There is sufficient variation in C. silvatica to merit the recognition of two subspecies (subsp. silvatica and subsp. disjuncta Brummitt) based on differences in the bracteoles, and one variety, var. quinquepartita N. Terrace, which has a corolla divided into several definite lobes. The variety is rare, having only been recorded in Britain on a few occasions and it might be referable to either of the two subspecies (Sell & Murrell 2009).

Strong vegetative and limited flowering reproduction

In common with C. sepium subsp. sepium, the even larger and more glamorous pure white flowers of C. silvatica are completely self-incompatible, a condition which limits the species' ability to set seed, especially in small populations. To an unknown extent, plants of C. silvatica must sometimes (often) be derived from fragments of the fleshy, almost succulent, brittle rhizomes and roots transported with soil, with the result that local stands may represent single strain clones (Salisbury 1962). Whenever a local colony of any dimension consists of just one or a few genetic strains, bee-transported compatible pollen may prove to be too distant, making it unavailable for fertilisation of the flowers.

Thus in both of these common species, the native C. sepium and the alien C. silvatica, vigorously spreading vegetative populations frequently fail to produce fruit and set no seed (Stace & Crawley 2015). Of course, some larger colonies will contain more than one strain and they can freely set fruit and develop abundant seed (Baker 1957a), but fortunately the reduction created by homomorphic incompatibility limits the dispersal and colonising abilities of the species to a considerable extent.

It is remarkable that three of the alien species most feared and hated by gardeners (C. silvatica, Veronica filiformis (Slender Speedwell) and Fallopia japonica (Japanese Knotweed) should be mainly or entirely vegetatively propagated due to their inability to set seed (Stace & Crawley 2015).

Any flowering that takes place is from July to September and pollination of the self-incompatible flowers is similar to C. sepium (Garrard & Streeter 1983) (see the C. sepium subsp. sepium account on this website). The fruit capsule of C. silvatica develops from September onwards into October. The capsule is 10-15 mm in size and sub-globose in shape, splitting when ripe to release the seeds, which are larger (4-5 mm in diameter), smoother and blacker than those of C. sepium subsp. sepium. Like the latter, they are hard-coated and presumably have similar powers of extended dormant longevity (Salisbury 1964; Sell & Murrell 2009). Having said that, there is a solitary observation of the species in the soil seed bank survey of NW Europe which suggests C. silvatica seeds are transient, surviving in the soil for less than one year (Thompson et al. 1997). However one record in that survey is insufficient to base a definite case on, since four of a total of nine records for C. sepium suggest it also has transient seeds, whereas other data findings in the same survey indicate buried seed survival in soil for up to 40 years (Thompson et al 1997).

Fermanagh occurrence

While elsewhere in B & I this is a rather common and widespread naturalised garden escape, there are only six widely spread records of it across Fermanagh spanning a 59-year period.

Apart from the first record listed above, the details of the other five Fermanagh finds are: roadside hedge at Gorteen, below Slieve Rushen, 18 July 1991, RHN; disused quarry on the outskirts of Ederny village, 3 October 2002, I. McNeill; Cloncoohy, 3 km SW of Teemore, 11 September 2010, RHN & HJN; S of Clonelty, 3 km SE of Newtownbutler, 15 September 2010, RHN & HJN; Necarne near Irvinestown, 18 September, RHN.

Since so few colonies of C. silvatica have been recorded in rural Fermanagh, seed production and its successful dispersal appears very much less likely here than in eastern NI. In urban Belfast, for instance, C. silvatica has become sufficiently common for Beesley & Wilde (1997) to record it in 40% of the 1-km squares in the inner city, some colonies demonstrating high levels of vegetative vigour and dominance, although not as common as C. sepium anywhere across the city, and especially so on waste ground.

Irish occurrence

The pattern of occurrence or recording of this clambering rhizomatous perennial in Ireland is very patchy and uneven. The Cen Cat Fl Ir 2 lists it as having been recorded in 30 of the 40 Irish VCs, to which Cat Alien Pl Ir adds two more; neither of these sources includes Fermanagh. After the announcement here of its rare presence in Fermanagh, the situation remains that C. silvatica has not yet been reported in seven other Irish VCs. The New Atlas hectad map shows C. silvatica present in most maritime and a proportion of inland squares up along the Irish Sea coast from E Cork (H5) to Co Londonderry (H40). However, it is much more thinly scattered up the Atlantic west coast and inland, stretching northwards from Mid-Cork (H4) to E Donegal (H34).

Although it may sometimes be mistakenly recorded as either C. sepium or C. pulchra (Hairy Bindweed), the existing pattern of Irish records suggests that C. silvatica might still be slowly spreading on the island and may well be under-recorded.

British occurrence

In most parts of lowland, populated B & I the species is now well established and naturalised in woods and hedgerows. This is especially so in lowland England and Wales as far north as Cumberland (VC 70) and Cheviot (VC 68), although it remains very much more scarce and patchy in lowland Scotland except up the E coast, and in the major conurbations of Glasgow and Edinburgh. The distribution appears to be stable, rather than increasing or decreasing (Rich & Woodruff 1990; Clement & Foster 1994; Preston et al. 2002). There is a separation in distribution between the two subspecies, subsp. disjuncta being the more common form throughout most of Britain, whereas subsp. silvatica appears the more frequent of the two on the Celtic fringe of Cornwall, Wales, parts of Scotland and all of Ireland (G.M. Kay, in: Preston et al. 2002; Sell & Murrell 2009).

European and world occurrence

Subsp. disjuncta is a native of the W Mediterranean region while subsp. silvatica is from the E Mediterranean. As C. sepium subsp. silvatica (Kit.) Maire, the range of C. silvatica is described as S Europe including the Mediterranean basin, N Africa and SW Asia including the Caucasus (Hultén & Fries 1986, Map 1537; Clapham et al. 1987).

Threats

Since only six colonies of C. silvatica have been recorded in rural Fermanagh, seed production and successful species dispersal appears very much less likely here than in urban parts of eastern NI.

Threats

None.

• Find out more about the format of the species accounts
• View abbreviations
• View references for all species accounts
• View a gazetteer of all the sites