Virginia creeper (Parthenocissus quinquefolia) vs false Virginia creeper (P. quinquefolia)
Are they two distinct species? Or just varieties? Or just the same?
Do anyone has the conclusive evidences to state that they are equal or different?
I would need evidences from scientific papers such as morphometric or genetic ones, not data from electronic databases.
Here’s one molecular take (note that they’re using the old synonym P. vitacea for P. inserta):
“The three species from the New World form a robust clade with BP = 100% and PP = 100% ( Fig. 2 ). Morphologically, this clade is characterized by their leaves with 5 – 7 leafl ets. Accessions of Parthenocissus vitacea and the narrow endemic P. heptaphylla (restricted to Texas, United States) form a clade that is nested within the group of the widely distributed P. quinquefolia ( Fig. 2 ). Parthenocissus vitacea and P. heptaphylla are morphologically similar to P. quinquefolia with overlapping distribution. The main difference between P. vitacea and P. quinquefolia is that the tendrils of P. vitacea do not have sticky pads ( Brizicky, 1965 ). Thus, Parthenocissus vitacea does not climb smooth walls, although it successfully climbs shrubs and trees. Parthenocissus heptaphylla differs from the other two by its 6 – 7 leafl ets. Together with morphological and biogeographic evidence, it seems reasonable to recognize P. vitacea and P. heptaphylla each as distinct species. Yet, we need further populational and phylogeographic analyses to better understand the evolutionary diversification of Parthenocissus in the New World.”
Nie Z.-L, Sun H., Chen Z.-D., Meng Y., Manchester S. R. & Wen J. (2010): Molecular phylogeny and biogeographic diversification of Parthenocissus (Vitaceae) disjunct between Asia and North America. – Am. J. Bot. 97/8: 1342–1353. DOI: 10.3732/ ajb.1000085
The interesting question raised by this phylogeny is whether the samples from central america nest P. heptaphylla and P. inserta within a broader P. quinquefolia, or whether the central american material is evolutionarily distinct from P. quinquefolia as well, perhaps basal to the three north american species that may have diversified as a consequence of repeated glaciation cycles. I wasn’t able to find any papers newer than this, but I’d suggest that when this gets a closer look with newer techniques you’re more likely to see additional splitting than any lumping. Given the significant morphological differences (in fruits and inflorescence structure, not just the tendril pads) it’s especially unlikely you’ll ever see P. inserta lumped under P. quinquefolia again.