Pterocarya fraxinifolia (Lam.) Spach. (syn.: P. caucasica C.A. Mey., P. sorbifolia Dippel) (Caucasus, N-Iran) – A very rare but increasing escape from cultivation. Records of Pterocarya fraxinifolia are double in Belgium: planted specimens often abundantly reproduce clonally (from suckers) and become more or less naturalised, especially in old parks but sometimes also in more natural environments, for instance in the valley of river Meuse in Hastière - île de Waulsort (Saintenoy-Simon & Duvigneaud 1994) or on the verge of marshy woodland by a canal in Landegem (June 2009). On the other hand recorded from 2005 onwards in riparian habitats without obvious vector of introduction. At first seen along river Lys (Leie) near Comines-Warneton and subsequently confirmed at several other, widely dispersed locations (Oeselgem, Wervik, Warneton, Deûlemont,…; Verloove 2011). In 2008 also observed along river Schelde near Kerkhove and Appels and since 2012 by the canal Roeselare-Leie, near Roeselare. Most specimens represent young, non-flowering and single-stemmed trees but in Oeselgem and Kerkhove Pterocarya fraxinifolia has built up vast populations as a result of strong clonal growth. It is becoming naturalised locally and probably exists elsewhere in Belgian riparian habitats. The origin of these plants remains uncertain: no parental plants have been observed in the vicinity. However, mature and freely fruiting trees of Pterocarya fraxinifolia (obviously also escapes from cultivation) have been recorded along river Deûle in northern France, close to its confluence with river Lys (Verloove 2011). At least the plants currently found along river Leie (Lys) probably originate there.
Most Belgian records seem to pertain to genuine Pterocarya fraxinifolia although other species might be involved (see under Pterocarya xrehderiana.
Pterocarya fraxinifolia probably mostly reproduces clonally in western Europe but sexual reproduction was recently also observed in Belgium and the Netherlands (and doubtlessly elsewhere as well) (see Andeweg 2013).
Selected literature
Adolphi K. (1995) Neophytische Kultur- und Anbaupflanzen als Kulturflüchtlinge des Rheinlandes. Nardus 2: 272 p.
Adolphi K. (1997) Neophytische Kultur- und Anbaupflanzen als Kulturflüchtlinge des Rheinlandes, 1. Nachtrag. Osnabr. Naturwiss. Mitt. 23: 27-36.
Andeweg R. (2013) Kaukasische vleugelnoot komt uit de schaduw. Straatgras 25(2): 36-37.
Campos J.A. & Herrera M. (2008) Diagnosis de la flora alóctona invasora de la C.A.P.V. Dirección de Biodiversidad y Participación Ambiental. Departamento de Medio Ambiente y Ordenación del Territorio. Gobierno Vasco, Bilbao: 296 p.
Campos J.A. & Herrera M. (2009) Análisis de la flora alóctona de Bizkaia (País Vasco, España). Lazaroa 30: 7-33.
Saintenoy-Simon J. & Duvigneaud J. (1994) L’île de Waulsort (Hastière, province de Namur). Les Naturalistes Belges 75(1): 26-32.
Schmid M. (2005) Untersuchung zur neophytischen Gehölzflora im Stuttgarter Stadtgebiet. Jh. Ges. Naturkde. Württemberg161: 178-257.
Verloove F. (2011) Fraxinus pennsylvanica, Pterocarya fraxinifolia en andere opmerkelijke uitheemse rivierbegeleiders in België en NW-Frankrijk. Dumortiera (in press).