Solanum carolinense
2. Solanum carolinense L. (N-Am.) – A rare and ephemeral alien (sometimes possibly persisting for some years). First seen as a wool alien in the Vesdre valley in 1947. Frequently recorded between 1993 and 1996 in port areas in Antwerpen and Gent, always associated with soybeans (Verloove & Vandenberghe 1994). Persisted for some years by a demolished oil mill along Albertkanaal at Merksem, at least between 1994 and 1996 (now gone). For quite some time no longer seen until it was recorded again at the Ghent Grain Terminal in the port area in Gent in 2013. Solanum carolinense recently tends towards naturalization in parts of Europe. In the Netherlands is has been reported as more or less persisting on river shores (see for instance Dirkse & al. 2008). However, it seems to thrive best in agricultural fields, especially in maize. Recent naturalization events have been noticed in Austria, Germany and Italy (Eberwein & Litscher 2007, Follak & Strauss 2010, Klingenhagen & al. 2012).
Flower colour is variable in Solanum carolinense. Plants with pale violet corollas belong to the typical form (f. carolinense), those with white corollas to f. albiflorum Benke. Both have been recorded in Belgium.
Another North American species, Solanum dimidiatum Rafin., might have been overlooked. It is exceedingly similar to Solanum carolinense but has larger corollas (30-40 mm across versus 20-30 mm) and stellate hairs on lower leaf surface with 6-8 rays (versus 2-5 rays).
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Selected literature:
Bassett I.J. & Munro D.B. (1986) The biology of Canadian weeds. 78. Solanum carolinense L. and S. rostratum Dunal. Can. J. Pl. Sci. 66: 977-991. [available online at: http://pubs.aic.ca/doi/pdf/10.4141/cjps86-120]
Dirkse G.M., Holverda W.J., Hochstenbach S.M.H. & Reijerse A.I. (2008) Solanum carolinense L. en Pimpinella peregrina L. in Nederland. Gorteria 33: 21-27.
Eberwein R.K. & Litscher T. (2007) Solanum carolinense L. (Solanaceae), ein gefährlicher Neubürger in Österreich. Rudolfinum - Jahrbuch des Landesmuseums Kärnten 2005: 225-330. [available online at: http://www.botanik.univie.ac.at/hbv/download/artenschutz_solanum_c.pdf]
Follak S. & Strauss G. (2010) Potential distribution and management of the invasive weed Solanum carolinense in Central Europe. Weed Research 50: 544–552.
Klingenhagen G., Wirth M., Wiesmann B. & Ahaus H. (2012) Occurrence of horse nettle (Solanum carolinense L.) in North Rhine-Westphalia. Julius-Kühn-Archiv 434: 601-604. [available online at: http://pub.jki.bund.de/index.php/JKA/article/view/1788/2129]
Verloove F. & Vandenberghe C. (1994) Nieuwe en interessante graan- en veevoederadventieven voor de Belgische en Noordfranse flora, hoofdzakelijk in 1993. Dumortiera 58-59: 44-59.
Wahlert G.A., Chiarini F. & Bohs L. (2014) Phylogeny of the Carolinense Clade of Solanum (Solanaceae) Inferred from Nuclear and Plastid DNA Sequences. Syst. Bot. 39(4): 1208-1216. [available online at: http://www.bioone.org/doi/full/10.1600/036364414X682599]
Wahlert G.A., Chiarini F.E. & Bohs L. (2015) A Revision of Solanum Section Lathyrocarpum (the Carolinense Clade, Solanaceae). Syst. Bot. 40(3): 853-887. [available online at: http://www.bioone.org/doi/pdf/10.1600/036364415X689302]