Echium L.
Echium is a genus of ca. 60 species. It is by far most divers in Macaronesia and further occurs in the Mediterranean area, West-Asia and South-Africa. Only one species, Echium vulgare L., is native in Belgium. Several species are cultivated as ornamentals in Europe (Cox 2000) but most are frost-sensitive.
Native Echium vulgare is a very variable species. Plants with aberrant colour and size of the corollas, a different indumentum,… could represent non-native forms or even other, related species (e.g. Echium rosulatum Lange as per Stace 2010).
1 Corolla only hairy on veins and margins (outside), ca. 18-30 mm across. Usually only two stamens exserted. Basal leaves ovate === Echium plantagineum
Corolla uniformly hairy, ca. 10-20 mm across. Usually 4-5 stamens exserted. Basal leaves lanceolate (native) === E. vulgare
References:
Cox C.J. (2000) Echium. In: Cullen J. & al. (eds.), The European Garden Flora, vol. 6. Cambridge University Press, Cambridge: 144-146.
Gibbs P.E. (1971) Taxonomic studies on the genus Echium, 1. An outline revision of the Spanish species. Lagascalia 1: 27-82. [available online at: http://institucional.us.es/revistas/lagascalia/01/02%20gibbs.pdf]
Gibbs P.E. (1972) Echium. In: Tutin T.G. & al. (eds.), Flora Europaea, vol. 3. Cambridge University Press, Cambridge: 97-100.
Piggin C.M. (1977) The herbaceous species of Echium (Boraginaceae) naturalized in Australia. Muelleria 3: 215-244.
Retief E. & Van Wyk A.E. (1998) The genus Echium (Boraginaceae) in southern Africa. Bothalia 28(2): 167-177.
Stace C. (2010) New flora of the British Isles, 3th ed.: XXXII + 1232 p. Cambridge University Press.
Valsecchi F. (1977) Contributo alla conoscenza del genere Echium: 1. Echium della Sardegna. Webbia 32(1): 101-127.
Van Ooststroom S.J. & Reichgelt Th.J. (1961) Enige voor België nieuwe adventieven. Bull. Jard. Bot. Etat Brux. 31: 431-441.