Lobelia L. (incl. Pratia Gaudich.)
Lobelia, as currently understood (see Mabberley 2008), is a genus of ca. 300 species from the warm-temperate and tropical regions of the world (predominantly in the Americas). Species of Pratia are now included in Lobelia (Lammers 2007a,b; Lammers 2011). Several species of Lobelia (and Pratia) are cultivated as ornamentals in Europe (see Ayers 2000). Two species of Lobelia are very rare natives in Belgium: L. dortmanna L. and L. urens L. The residence status of the latter is somewhat dubious. It has occurred in natural habitats in Boortmeerbeek and Howardries (Nef 1951) but is now probably extinct. Similar records in the Netherlands proved to belong with the similar but American Lobelia inflata L. (van der Meijden & Vermeulen 1994). Herbarium specimens from Boortmeerbeek have been confirmed as Lobelia urens; from Howardries no voucher specimens have been preserved apparently.
Downingia elegans (Lindl.) Torr., a tiny Lobelia-like species originating in western North America, has repeatedly occurred as a lawn weed in parts of Europe (Lenski 1984, Briggs & Fitzgerald 1986, Lenski 1987) and might be overlooked in Belgium. Like Lobelia erinus it is annual, sometimes procumbent with blue corollas. However, its corolla tube is not split to base on one side and its leaves are always narrower (linear to elliptic against obovate in Lobelia erinus). It should be looked for in recently sown lawns.
1. Prostrate creeping herb, rooting at the nodes. Corolla minute (6-8 mm), pale lavender to white, on long slender pedicels up to 80 mm long. Fruit (probably not produced in Belgium) a berry === 2. Lobelia pedunculata
1. Ascending to erect herb, never rooting at the nodes. Corolla larger (10-32 mm), most often blue. Fruit a capsule === 2
2. Nearly all leaves in a basal rosette. Plant usually submersed (native) === L. dortmanna
2. Stem leafy. Plant terrestrial === 3
3. Ascending to erect, small annual, up to 30 cm long. Pedicels long and slender, the longest (lowermost) at least 20 mm long === 1. L. erinus
3. Erect perennial, up to 130 cm tall. Pedicels short and thick, at most 12 mm long === 4
4. Corolla 10-15 mm long, blue. Leaves ca. 2-10 cm x 10-15 mm (native) === L. urens
4. Corolla 20-32 mm long, blue to violet (rarely white). Leaves ca. 2-16 cm x 3-75 mm === 5
5. Leaves lanceolate, 3-15 mm wide, glabrous and slightly leathery === 3. L. sessilifolia
5. Leaves ovate to narrowly oblong, 15-75 mm wide, glabrous to sparsely hairy, not leathery === 4. L. siphilitica
Literature
Ayers T.J. (2000) Lobelia and Pratia. In: Cullen J. & al. (eds.), The European Garden Flora, vol. 6. Cambridge University Press, Cambridge: resp. 499-501 and 496-498.
Briggs M. & Fitzgerald R. (1986) Aliens and adventives. Downingia elegans refound in East Sussex. BSBI News 44: 20-21.
Jäger E.J., Ebel F., Hanelt P. & Müller G. (eds.) (2008) Rothmaler Band 5. Exkursionsflora von Deutschland. Krautige Zier- und Nutzpflanzen. Springer Verlag, Berlin: 880 p.
Lambinon J., Delvosalle L., Duvigneaud J. (avec coll. Geerinck D., Lebeau J., Schumacker R. & Vannerom H. (2004) Nouvelle Flore de la Belgique, du Grand-Duché de Luxembourg, du Nord de la France et des Régions voisines (Ptéridophytes et Spermatophytes). Cinquième édition. Jardin botanique national de Belgique, Meise: CXXX + 1167 p.
Lammers T.G. (2007a) Campanulaceae. In: Kadereit J.W. & Jeffrey C. (eds.), The families and genera of vascular plants, vol. 8. Springer Verlag, Berlin: 26-56.
Lammers T.G. (2007b) World checklist and bibliography of Campanulaceae. Kew Publishing: 675 p.
Lammers T.G. (2011) Revision of the infrageneric classification of Lobelia L. (Campanulaceae: Lobelioideae). Ann. Missouri Bot. Gard. 98: 37-62.
Lenski H. (1984) Downingia elegans (Dougl.) Torr. – eine mit Grassaatgut eingeschleppte Adventivpflanze. Gött. Flor. Rundbr. 18: 75-77.
Lenski H. (1987) Nachtrag zu Downingia elegans (Douglas) Torr. Flor. Rundbr. 21: 24.
Mabberley D.J. (2008) Mabberley’s plant-book (3th ed.). Cambridge University Press, Cambridge: XVIII + 1021 p.
Nef L. (1951) Lobelia urens L. dans le Tournaisis. Lejeunia 15: 111-115.
Van der Meijden R. & Vermeulen J.J. (1994) Over Lobelia inflata L. en L. urens L. (Campanulaceae). Gorteria 20: 105-108.
Wimmer F.E. (1943) Campanulaceae-Lobelioideae, I. Teil. In: Mansfeld R. (ed.), Das Pflanzenreich IV.276b. Engelmann, Leipzig: 1-260.
Wimmer F.E. (1953) Campanulaceae-Lobelioideae, II. Teil. In: Mansfeld R. (ed.), Das Pflanzenreich IV.276b. Akademie Verlag, Berlin: 261-813.