Morus alba

Morus alba L. (C to E As.) – A regularly planted ornamental tree, although possibly less frequently so nowadays. Recorded in the 19th century as an escape on an old wall of the Jardin Botanique in the city of Brussels. Very rarely seen in recent times outside of cultivation. In 2017 a single, obviously spontaneous individual was found between stone blocks of river Schelde in Berlare (Uitbergen). It is unknown whether this plant arrived there as washed-up rhizome or germinated from seed.

The exact identity of the plants currently found in Belgium (including those recently seen in the wild) is uncertain. According to Tison & de Foucault (2014) Morus kagayamae Koidzumi (syn.: M. alba ‘Macrophylla’) is naturalizing in France in riparian habitats. It has larger leaves than M. alba (usually more than 10 cm long) that are more deeply and narrowly lobed and hairless shoots (Tison & de Foucault l.c., Nelson 1997). Roloff & Bärtels (2006), on the contrary, state that ‘Macrophylla’ usually has undivided leaves. The plant from Berlare has large, deeply lobed leaves and hairless shoots and belongs to M. kagayamae. However, Laguna Lumbreras & Ferrer Gallego (2012) argued that M. kagayamae and M. alba can only be reliably separated based on style length of the female flowers, while planted trees in Spain usually are sterile (‘fruitless’) only bearing male flowers. Some of the plants there may also represent hybrids of M. alba and M. kagayamae. Pending further study Belgian plants with glabrous upper leaf surfaces are referred to as M. alba s.l., probably including hybrids and/or cultivars.

Selected references

Andreas A. (2013) Zum Vorkommen von Maulbeeren (Morus sp., Moraceae) in Nordwest-Sachsen. Mitteilungen der Deutschen Dendrologischen Gesellschaft 98: 205-213.

Delucchi G. (1989) Morus alba (Moraceae), ampliación de su área geográfica en Argentina y observaciones sobre su naturalización. Darwiniana 29(1-4): 405-406. [available online at: https://www.researchgate.net/publication/263009626_Morus_alba_Moraceae_a...

Höcker R. & Wolf S. (2014) Weisse Maulbeerbäume (Morus alba L.) als Kulturrelikte regionaler Seidenproduktion in Ansbach. RegnitzFlora - Mitteilungen des Vereins zur Erforschung der Flora des Regnitzgebietes 6: 36-54. [available online at: http://www.regnitzflora.de/band6/RegnitzFlora-6_Hoecker_Wolf.pdf]

Laguna Lumbreras E. & Ferrer Gallego P.P. (2012) Sobre la identidad de Morus alba var. kagayamae, planta alóctona ornamental en España. Bouteloua 18: 36-43. [available onlin at: http://www.floramontiberica.org/Bouteloua/Bouteloua_18.pdf]

Nelson E.C. (1997) Morus. In: Walters S.M. & al. (eds.), The European Garden Flora, vol. 3. Cambridge University Press, Cambridge: 86-87. 

Rao C.K. & Jarvis C.E. (1986) Lectotypification, taxonomy and nomenclature of Morus alba, M. tatarica and M. indica (Moraceae). Taxon 35(4): 705-708.

Roloff A. & Bärtels A. (2006) Flora der Gehölze (2e Auflage). Ulmer, Stuttgart: 844 p.

Tison J.-M. & de Foucault B. (coord.) (2014) Flora Gallica. Flore de France. Editions Biotope, Mèze : xx + 1196 p.