Identity
Parthenocissus quinquefolia s.str., excluding P. inserta.
The two species can best be distinguished by their inflorescences and tendrils. The inflorescence of P. inserta is more robust and almost dichotomous, whereas that of P. quinquefolia is more delicate and as a rule more panicle-like (this is not very clear on the picture above). The fruits of P. inserta are almost globose, while that of P. inserta are more or less pyriforme and smaller. The tendrils of P. inserta are more robust, too, and usually have 3–4 branches, whereas those of P. quinquefolia are more fragile and most often have 5–8 branches.
Other features are not that reliable. In particular, while the tendrils of P. quinquefolia almost ever end in a adhesive disc, it is not uncommon to P. inserta to have that discs, too. They will be formed only when the tendrils come in contact with a wall or similar surfaces.
Recent Information on the situation in east Austria
Parthenocissus quinquefolia in Central Europe is a much less frequent neophyte as P. inserta, but recent observations strongly indicate that it is fully naturalised at least in smaller parts of Vienna, especially near the Danube. Here it is not uncommon for both species to grow together. Outside of Vienna I so far only have seen P. inserta.