x Reyllopia conollyana (J.P. Bailey) Galasso (syn.: Fallopia x conollyana J.P. Bailey; Fallopia baldschuanica x Reynoutria japonica) (Hybr.) – A very rare alien, recorded thus far in two localities in Belgium. First observed on a talus slope in Izegem in 2016 and later in the same year also alongside a railway track near Gent (Hoste & al. 2017). These records refer to established plants. In addition, this hybrid has also been recorded as open pollinated seed from F. japonica. It is probably not rare as such but, for some reason, rarely establishes itself in the wild.
x Reyllopia conollyana is evidently intermediate between both, morphologically quite different parents. However, it is obviously closer to Reynoutria japonica. It is distinguished from the latter by its leaves that are narrower with a long-acuminate apex, the thinner stems that are bowing at ends and the somewhat larger corollas.
Bailey J.P. (2001) Fallopia × conollyana The Railway-yard Knotweed. Watsonia 23: 539-541. [available online at: http://archive.bsbi.org.uk/Wats23p539.pdf]
Hoste I., Verloove F. & Bailey J.P. (2017) Two recent records from Belgium of established plants of Fallopia ×conollyana: A low profile alien steps into the open. Dumortiera (in prep.).