2. Pterocarya x rehderiana C.K. Schneider (P. fraxinifolia x P. stenoptera DC.) (Cult.) – A very are escape from cultivation but possibly overlooked. A single juvenile specimen was recorded on the gravely banks of river Maas near Lanaken in 2011 (see: http://waarnemingen.be/waarneming/view/61236611#). A taller tree grows on the banks of river Leie in Harelbeke (2019). In this area P. fraxinifolia is well-naturalized and spreading which means that both taxa may have been intermingled. Previous claims (from a park in Brussels in 1995) probably did not refer to “genuine” escapes but were mere suckers from a planted specimen.
The distinction of Pterocarya fraxinifolia, Chinese P. stenoptera and its hybrid is not always straightforward. Invasive populations of Pterocarya from northern Spain have been ascribed to both P. stenoptera and P. x rehderiana (see Campos & Herrera 2008, Campos & Herrera 2009). The plant from Lanaken was eventually assigned to Pterocarya x rehderiana on behalf of the presence of a terminal leaflet. This is usually absent in Pterocarya stenoptera. According to Wijnands (1989) this hybrid is hardier than either parent.
Selected literature:
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.
Wijnands D.O. (1989) Pterocarya. In: Walters S.M. & al. (eds.), The European Garden Flora, vol. 3. Cambridge University Press, Cambridge: 20.