Juglans nigra L. (N-Am.) – A very rare escape from cultivation. Juglans nigra is regularly cultivated as a curiosity or (very rarely) for timber. It locally persists (even in nature reserves) but, so far, hardly reproduces. Most records therefore surely represent relics from cultivation. However, Juglans nigra was discovered along river Schelde near Berchem-Kerkhove in 2008 (one spontaneous specimen, between basalt rocks just above waterline; confirmed in fruit in 2010) (Verloove 2011). Furthermore discovered in relative abundance by the Albertkanaal near the Sint-Pietersberg in 2009, along with Quercus cerris (comm. R. Barendse; planted and freely escaping in the surroundings, juvenile specimens growing tall and possibly becoming naturalised). Since 2010 also seen along river Leie between Wervik and Menen (several young trees between basalt rocks), on a talus slope adjoining motorway E17 near Kortrijk (scattered young individuals) and in several other places in the southernmost part of the province of West-Flanders. Juglans nigra is obviously on the increase in Belgium and a future naturalization is very likely. See here for an up-to-date overview of Belgian records with many additional useful photographs: http://waarnemingen.be/soort/view/20392.
Juglans nigra is also increasingly escaping elsewhere in Europe (see for instance Bull 2007, Clement 2007).
The exact identity of the trees currently found in the wild in Belgium is somewhat critical. On a single tree leaves with a well-developed as well as with (almost) lacking terminal leaflet occur. Also, the amount of glandular hairs of the leaves seems to be higher than it should be in J. nigra. These are characters that would suggest an influence of J. cinerea and perhaps our plants are hybrids of these species. Such hybrids are known to be more vigorous than either parent (see also Farlee & al. 2010).
Bull A. (2007) Juglans nigra in Norfolk. BSBI News 104: 35.
Clement E.J. (2007) Juglans nigra established on the River Thames towpath (Surrey). BSBI News 103: 33.
Farlee L., Woeste K., Ostry M., McKenna J. & Weeks S. (2010) Identification of Butternuts and Butternut Hybrids: 11 p. Forestry and Natural Resources 420 [available online at: https://www.extension.purdue.edu/extmedia/FNR/FNR-420-W.pdf]
Verloove F. (2011) Fraxinus pennsylvanica, Pterocarya fraxinifolia en andere opmerkelijke uitheemse rivierbegeleiders in België en NW-Frankrijk. Dumortiera (in press).