BSBI Species Accounts ArchiveCalystegia sepium
Thu, 08/12/2010 - 13:27 | 
markd
Calystegia sepium (L.) R. Br., Hedge Bindweed, is the commonest of all the bindweeds that occur in the British Isles. The range of common names used for these species is highly confusing and it is better to stick to scientific names to avoid ambiguity. It is easily confused with Calystegia silvatica, which is a very similar species that has been introduced from the Mediterranean region, and was not recognised as a separate species until 1948. The two are distinguished by their bracteoles, which overlap in C. silvatica but do not in C. sepium. Other bindweeds that occur in Britain include Convolvulus arvensis, which is normally an arable weed, and Hairy Bindweed, Calystegia pulchra, which has overlapping bracteoles and pink flowers. There are several subspecies of C. sepium in the British isles:
- ssp. sepium is the common form with glabrous white or (sometimes) pink flowers.
- ssp. roseata has pubescent stems and pedicels and pink flowers.
- ssp. spectabilis has pink flowers and a rounded basal leaf sinus. It has only been recorded in one place (in North Wales), but Stace (1997) suggests that it may have been overlooked elsewhere.
Chromosome No.: 2n = 22 (Stace 2010).
Widespread thoughout the British Isles except in the Highlands and the north of Scotland.
Calystegia sepium
Photograph: A.J. Lockton.
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Calystegia sepium sl.
Calystegia sepium ssp. sepium
Calystegia sepium ssp. roseata
Calystegia silvatica
Grime, Hodgson & Hunt (2007) provide a detailed account of the ecology of the common subspecies, C. sepium ssp. sepium. The other, ssp. roseata, is a plant of saltmarsh and maritime grassland. C. sepium ssp. sepium is recorded on riverbanks, road verges, waste places, manure heaps, rubble, hedges and mires, but is apparently absent from woodland (ibid.). In undisturbed semi-natural vegetation, such as reedbeds, it is an inconspicuous and non-invasive component of the vegetation; but in abandoned gardens and spoil heaps it can become extremely abundant, smothering other plants. This seems to be dependent on a level of soil disturbance, which allows it to reproduce by fragments of rhizomes or roots. Sexual reproduction is much less significant and, as plants are self-incompatible, seed set is often poor. Rodwell (1991-2000) gives quite a few NVC communities for C. sepium, including three woodland types: W2, W5 and W21. He also gives numerous swamps and mires. Here is the full list: M22, M27, S4, S5, S6, S13, S21, S24, S25, S26, S28, SM28, OV13, OV25, OV26, OV27, OV30 and OV42. Rodwell (op. cit.) does not give any communities for C. silvatica or C. sepium ssp. roseata, so one must assume that the above apply to C. sepium agg. - a loose term for any of these three taxa. This is unfortunate, as each clearly has a very distinct ecology.
Calystegia silvatica
Photograph: A.J. Lockton
Recorders might want to be alert to the possible presence of C. sepium ssp. spectabilis - eFloras has an illustration from the Flora of China. For many years no-one noticed that C. sepium and C. silvatica were different species, and it seems quite likely that confusion still occurs, especially in ecological descriptions. This is made more complicated by the fact that the two species hybridize freely and form hybrid swarms that can be very close in appearance to either parent (Stace 1961). Most authors seem to agree that C. sepium is more common in semi-natural habitats and that C. silvatica is the more rampant weed of gardens and arable fields. Further study could therefore be quite rewarding.
- Stace, C.A. 1961. Some studies in Calystegia: compatibility and hybridisation in C. sepium and C. silvatica. Watsonia 5, 88-105.
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