Sambucus canadensis L. (syn.: S. nigra subsp. canadensis (L.) Bolli, S. nigra var. canadensis (L.) B.L. Turner) (N-Am.) – A rare but probably overlooked escape from or relic of cultivation. Apparently first collected in the wild in 1972 in Mechelen (land fill) but possibly overlooked before. There is a remarkable concentration of records in the Kempen (see http://waarnemingen.be/soort/maps/7405?from=2012-01-17&to=2013-01-17) where it grows in deciduous woodland in similar habitats like native S. nigra (nitrophilous, rather damp shady places). Records are available from Balen, Geel, Genk, Ham, Hechtel-Eksel, Kasterlee, Meerhout, Mol, Olmen, etc. It seems that Sambucus canadensis was formerly regularly planted on pond margins and now persists (as a relic) or spreads in the surroundings (dispersed by berry-eating birds). Outside of this area it seems to be virtually absent although it might have been widely overlooked.
Bolli (1994) reduced Sambucus canadensis to a subspecies of S. nigra. However, this taxonomy is not supported by recent molecular phylogenetic research (Clarke & Tobutt (2006). Distinction of these two species is not always straightforward. Fruit colour seems to be the best feature (see key) although fruits ultimately also turn dark purplish in Sambucus canadensis. In addition, it always has more leaflets (often slightly but distinctly paler beneath and sometimes leaves are twice pinnate) and nutlets are also more numerous. Moreover, Sambucus nigra tends to be a single or few trunked large shrub or small tree, whereas S. canadensis can have many stems and can aggressively spread by underground rhizomes (Finn & al. 2008).
Sambucus canadensis in the sense of Thunb., an illegitimate name, refers to a very different species from Southeast Asia for which the correct name seems to be S. javanica Blume (Cann 2000).
Literature: Weeda (1978), Bolli (1994), Cann (2000), Clarke & Tobutt (2006), Finn & al. (2008).
Bolli R. (1994) Revision of the genus Sambucus. Diss. Bot. 223: 1-227.
Cann D.C.G. (2000) Sambucus. In: Cullen J. & al. (eds.), The European Garden Flora, vol. 6. Cambridge University Press, Cambridge: 416-418.
Clarke J.B. & Tobutt K.R. (2006) Development of microsatellite primers and two multiplex polymerase chain reactions for the common elder (Sambucus nigra). Molecular Ecology Notes 6(2): 453-455.
Finn C.E., Thomas A.L., Byers P.L. & Serçe S. (2008) Evaluation of American (Sambucus canadensis) and European (S. nigra) Elderberry Genotypes Grown in Diverse Environments and Implications for Cultivar Development. HortScience 43(5): 1385-1391. [available online at: http://hortsci.ashspublications.org/content/43/5/1385.full.pdf+html]
Weeda E.J. (1978) Sambucus canadensis L. bij Bentveld, verwilderd (?). Gorteria 9(3): 67.