Calystegia sepium subsp. roseata
Brummitt, a bindweed
Account Summary
Introduction, history unknown, a very rare casual, but possibly an identification error.
1 October 1995; McNeill, I.; edge of laneway, Gushedy Beg Td, N of Ederny.
This subspecies differs from subsp. sepium in its deep pink, white-striped flowers and in having short hairs on stems, leaf-stalks and flower-stalks (An Irish Flora 1996). It is principally a coastal plant of salt-marshes and maritime sands, native of W Europe and local on W coasts of B & I (R.K. Brummitt, in: Tutin et al. 1972, Flora Europaea 3, 78-9; New Flora of the BI 1997). It also occasionally occurs elsewhere, apparently introduced and naturalised. This taxon has previously been recorded in the NE of Ireland at two coastal sites in the extreme N of Antrim (H39) (FNEI 3), but never inland or indeed landlocked as is the situation in county Fermanagh. There are also a number of sites for this subspecies in W Donegal (H35), along the northern shore of Donegal Bay, which is not very distant from Fermanagh (Perring & Sell 1968, map 406/1b).
The similarity of the plant to C. pulchra (Hairy Bindweed) means that care in identification is required, but the latter has bracteoles below the calyx that are overlapping and strongly inflated, while subsp. roseata has bracteoles that are not inflated and that scarcely overlap (An Irish Flora 1996).
Although Ian McNeill is an excellent field botanist, without a voucher to obtain verification, we cannot be certain that the identification of the solitary Fermanagh record listed above is correct. Accordingly, with regret, we can only regard this as a tentative First County Record.
Growth form and preferred habitats
Hedge Bindweed is a climbing, twining, tenacious perennial with large, heart-shaped leaves, thoroughly loathed by gardeners for its persistent, deeply penetrating roots and white rhizome that tangles itself among the roots of more desirable decorative subjects in the tended plot, always proving extremely difficult to eradicate. Herbicides such as 2,4-D offer some hope, since the species is moderately susceptible to its effect (Salisbury 1964).
The species, as currently understood, was united with Calystegia silvatica until the 1930s. Praeger (1934, 1936) seems to have been the first botanist in the British Isles to distinguish C. silvatica at Lough Gill, Co Sligo (H28) and the species group was further delimited and C. pulchra recognised and named in 1960 (Brummit & Heywood 1960).
Apart from the garden, typical habitats of the species range from hedges by roads, streams and rivers, waste ground, old quarries and in scrub woodland, both terrestrial and wetland fen carr. It also climbs (always twisting in an anti-clockwise direction) in reed-beds and on other tall vegetation in wet ditches, marshes and fens. It is in the latter, wetter habitats mentioned, that C. sepium subsp. sepium appears to be most truly indigenous in B & I (FNEI 2).
Under favourable growing conditions, the twining motion can be very rapid, the climbing stem completing a revolution in one to two hours. If no support is sufficiently close to climb upon, the Hedge Bindweed stems often twine around one another, producing a thick, rope-like structure that explains the name 'Ropewind' (Salisbury 1964). The species is a good indicator of fertile soil conditions and thus it never occurs in very acidic peat habitats (Hill et al. 1999). Grime et al. (1988, 2007) considered it was restricted to situations where the pH was above 5.5, which is the reaction typical of fertile topsoil in NI.
C. sepium subsp. sepium uses either the stout stems of tall herbs, shrubs and hedges, or artificial, man-made structures such as fences to climb and ascend to heights around 3 m or so above ground level. The plant can then sometimes form a dense, smothering, curtaining canopy over supporting vegetation in the latter part of the growing season. Moist, fertile growing conditions and a moderate degree of disturbance appear necessary to sustain a competitive balance between Hedge Bindweed and the potentially dominant tall, perennial herbs and shrubs on which it climbs. If the habitat is left undisturbed, shade builds up and C. sepium subsp. sepium tends to decline in vigour. It is then either incapable of flowering, or flowering ceases altogether if it becomes subjected to dense shade, as for instance frequently happens in undisturbed tall-herb fens and reed-beds. In autumn, the aerial shoot dies back, giving competing species some months of respite. The established strategy of C. sepium is categorised as intermediate between Competitor and Competitive-Ruderal (Grime et al. 1988, 2007).
Variation
Calystegia sepium s.l. is described as a polymorphic and widespread species that forms an "unusually complicated complex of closely related taxa, taken as species, subspecies, varieties or forms by different authors, who rarely agree on their limitation and geographical range" (Hultén 1974, Circumpolar plants II, p. 282). The critical Flora of B & I recognises three subspecies of C. sepium and two forma of subspecies sepium ; forma sepium with a white, undivided corolla and forma colorata (Lange) Dörfl., having a corolla with five pink 'windows' and undivided (Sell & Murrell 2009). 'Windows' appear to be coloured sections of the corolla, separated by white rib-like regions associated with the joins between the five fused petals.
Vegetative reproduction
In disturbed sites (and especially in gardens), the plant displays vigorous vegetative regeneration. Even very small fragments of rhizome or root prove capable of forming new plants and by this means the species can develop spreading clones that gradually build upon the growth achieved in previous years, thanks to its long-term persistence in disturbed ground and a very rapid growth rate in moist, fertile, productive sites, including recently abandoned or neglected corners of gardens (Grime et al. 1988, 2007).
Flowering reproduction
Seed reproduction is often secondary in importance to vegetative increase and spread in C. sepium subsp. sepium populations The solitary, axillary, bisexual, flowers are borne on flexuous, pedicels 2-21 cm long. The flowers are self-incompatible and when formed in small, single- or few-cloned colonies, developed by vegetative increase, seed set is frequently poor. However, where more numerous separate colonies of differing vegetative origin and strain occur in a locality, seed production is more frequent, as would be expected (Salisbury 1964).
The glamorous, white, funnel-shaped flowers, 3-7 cm in diameter, produced from June to September are the largest of any species in the flora of B & I. The five united petals that make up the corolla funnel have the five stamen filament bases fused to them at their base (ie they are epipetalous, meaning 'upon the petals'). Below the corolla base is the well-developed disc at the base of the superior ovary that secretes nectar. The flower is thus a 'revolver', with five narrow openings at the base of the corolla that allow insects to probe and suck up the nectar reward. On entering the corolla an insect bearing pollen from another flower will readily effect cross-pollination as it comes in contact with the 2-lobed stigma which projects beyond the surrounding stamens. Each solitary, open flower typically lasts for around a single day (but see below), and they open in regular sequence along the stem (Stace 1965).
The large, pure white corolla might suggest the flowers are evolved to attract night-flying (ie crepusclar) pollinators, such as moths. However, the corolla trumpet opens soon after sunrise and usually closes after 12-28 hours, depending upon whether or not pollination has been achieved and also upon the prevailing weather conditions – dull, wet or cold days prolong the duration of flower opening to a limited extent. The blossom is scentless, or only faintly scented, although it does offer both nectar (well concealed at the bottom of the corolla tube) and more freely obtained pollen food sources (Salisbury 1964; Stace 1965). Thus, although daytime visitors are relatively scarce, considering how conspicuous the large flowers are, they must be the important pollinators for the species (Salisbury 1964). The daytime visitors are chiefly bees (including bumblebees) and hoverflies, although if the flower has not been pollinated by nightfall, it remains open to visits from moths and other night-active pollinating insects until at least the second sunrise. Some flowers may thus remain open for around 48 hours. Flowers never close at night and re-open the next day. Not all insect visitors are pollinators, others may be seeking shelter, or are foragers and flower pests (Stace 1965; Proctor et al. 1996).
The fruit is a dehiscent, capsule and its development continues from September into October. The two large enveloping bracteoles and five small sepals appear to have no biological significance whenever the flowers are open and functioning, although they undoubtedly conceal and protect the developing flower when in bud, and the young fruit. This gains the species the English common name 'Hooded Bindweed' and also the genus name (see Names section below) (Grieve 1931; Stace 1965).
Fertile fruits contain from 1-4, large, rounded, dark brown or black seeds, 4-7 mm in diameter. The fact that the seeds are large and heavy limits their ability to disperse, although streamside populations may be transported by water (Ridley 1930). Were it not for sparse seed production, the species would be even more prevalent than is the case, particularly since the seed has great longevity. C. sepium seed, buried at a depth of 105 cm for 16 years, produced 70% germination. After 39 years burial, another sample achieved 53% germination (Salisbury 1964).
Hybrids
C. sepium readily forms hybrids with two introduced relatives, C. pulchra (Hairy Bindweed) and C. silvatica (Large Bindweed) that colonise hedges and waste places, mainly in urban areas and are widely naturalised in parts of B & I (New Atlas). These hybrids can form at least partially fertile clones, obviously complicating plant identification where they occur (Stace 1961, 2015). Fortunately these hybrids are rare or very rare in Ireland and none of them have ever been recorded in Fermanagh.
Fermanagh occurrence
In Fermanagh, subsp. sepium has been recorded in 191 tetrads, 36.2% of those in the VC. As the tetrad map clearly indicates, it is frequent and widely scattered throughout the more fertile lowland areas of the county to the N and W of Lough Erne, but rather scarce or absent from most of the ground lying to the SW of the major lakes, including the western plateau uplands.
British and Irish occurrence and status
In the not so distant past, the seed of this form was an occasional contaminant in sown agricultural mixtures, especially those that included vetches. Together with the strong association the species has with artificial rather than with natural habitats in B & I, this raises some doubt as to its native status (eg in Ireland, in Connemara and the Burren (H9 & H16) (Flora of Connemara and the Burren)).
Hedge Bindweed is common and is generally regarded as native throughout southern regions of B & I but in Scotland, north of Edinburgh and Glasgow, it becomes much more local and there it could be an accidental introduction.
There does not appear to be any unequivocal fossil pollen evidence from pre-Neolithic deposits in B & I, so very possibly it is a long-standing accidental introduction here too (Salisbury 1964; Godwin 1975; Webb 1985).
European and world occurrence
C. sepium is also considered native and is common throughout temperate regions of Europe, W Asia, N Africa and N America (Clapham et al. 1962). C. sepium subsp. sepium occurs as a casual introduction in Madeira (where it is very rare) and the species now occurs world-wide with many geographic subspecies, certainly in many instances occurring purely as an introduction (Ridley 1930; Hickman 1993). The species s.l. belongs to the discontinuous circumpolar plants, the map showing it introduced in the southern hemisphere in Africa Cape Province, Java, Australia, New Zealand and temperate S America (Hultén & Fries 1986, Map 1537; Sell & Murrell 2009).
Uses
All members of the Convolvulaceae have purgative properties to a greater or lesser degree and C. sepium subsp. sepium is used in both allopathy and homoeopathy to treat constipation and fevers (Launert 1981). The acrid roots of C. sepium are much more violently purgative than those of C. soldanellla (Sea Bindweed), and despite their drastic action, they were used by poorer people in place of the milder C. scammonia (Scammony) imported from the Levant. The use of C. sepium as a purgative goes right back in herbal literature to ancient Roman times and Dioscorides (Allen & Hatfield 2004). Having said this, although Grieve (1931) describes the plant in her book A Modern Herbal, she makes no mention of the medicinal use of the species.
The rhizome is boiled and eaten as a vegetable in China, and young leaves are likewise eaten as salad in India (Mabberley 1997).
Names
The genus name 'Calystegia' is derived from two Greek words, 'kalyx', a calyx or 'cup', and 'stege', 'a covering', probably referring to the two bracts that cover the calyx of some bindweeds (Johnson & Smith 1946; Gilbert-Carter 1964). The specific epithet 'sepium' is from the Latin, 'sepes', 'a hedge', referring to one of its most common habitats (Gledhill 1985).
The C. sepium complex as a whole has a great many common names. Grigson (1987), for example, lists a total of 60, most of which refer to its climbing habit (eg 'Bindweed', 'Bearbind', 'Ropewind' and 'Woodbine'), but the remainder of them stress either its beautiful flower ('Hedge Lily' and 'Old Man's Nightcap'), or else its troublesome character as a weed ('Devil's Garter', 'Devil's Vine' and 'Hellweed').
Threats
None.