Convolvulus dubius J. Gilbert (syn.: Calystegia pulchra Brumm. et Heywood) (Hybr.) – A very rare, ephemeral alien (although sometimes persisting for some time). First seen in Hofstade in 1931 and near Walcourt in 1935 (published as Calystegia silvatica by Lawalrée 1956). Subsequently collected near Watermaal-Bosvoorde in 1952 and in 1967 in Berchem (all as Convolvulus sepium). Discovered in an old hedge in Roeselare in 2008. Probably overlooked elsewhere. Convolvulus dubius is usually seen in hedges or shrubs, most often in the vicinity of houses.
Like other species in the Convolvulus sepium complex, C. dubius is rather variable, surely – at least in part – as a result of hybridisation. A few Belgian collections (from Berchem and Beveren) probably represent a putative hybrid of Convolvulus dubius and C. sepium (Calystegia xscanica Brummitt): they are characterised by peduncles unwinged and distinctly winged on the same plant, leaf base of variable shape (more or less square and rounded),….
Convolvulus dubius is an enigmatic taxon which origin long remained obscure. However, Brown & al. (2009) showed that a hybrid origin is very likely (a crossing of the Asian Convolvulus pellita (Ledeb.) G. Don and C. silvaticus subsp. silvaticus).
Bolbrinker P., Funk B. & Manitz H. (1975) Die Pracht-Winde (Calystegia pulchra) in Mittelmecklenburg. Bot. Rundbr. Bez. Neubrandenburg 5: 43-44.
Brown J.M., Brummitt R.K., Spencer M. & Carine M.A. (2009) Disentangling the bindweeds: hybridization and taxonomic diversity in British Calystegia (Convolvulaceae). Bot. J. Linn. Soc. 160: 388-401.
Brummitt R.K. & Heywood V.H. (1960) Pink-flowered Calystegiae of the Calystegia sepium complex in the British Isles. Proc. Bot. Soc. Brit. Isles 3: 384-388.
Gilbert J.L. (1963) Convolvulus dubius, nom. nov. J. Northamptonshire Nat. Hist. Soc. Field Club 34: 149-150.
Hellfeldt R. (1981) Zur Verbreitung der rosarot blühenden Calystegia-Arten in Schleswig-Holstein. Kieler Not. Pflanzenk. Schleswig-Holstein 13(3-4): 44-46.
Lawalrée A. (1956) Phanérogames adventices ou naturalisées en Belgique. Bull. Soc. Roy. Bot. Belg. 88: 25-28.
Verloove F. (2011) Weinig gekende Calystegia-taxa in België. Dumortiera (in press).