Major Long's sand dune grapes

This topic has been of some interest on the Grape Breeders' list.  Members of Major Stephen Long's 1820 expedition  wrote the following about what we now call Beaver Dunes park in Oklahoma ('A' in the below map).   This is on the edge of what I call 'local'.  Beaver Dunes park is a 6 hour drive north of me, in the Oklahoma panhandle. Put another way, it is 27 miles north of the Texas state line.

 "On examination we found these hillocks had been produced, exclusively by the agency of the grape vines arresting the sand, as it was borne along by the wind, until such quantities had been accumulated as to bury every part of the plant except the ends of the branches.  Many of these were so loaded with fruit, as to present nothing to the eye but a series of clusters so closely arranged as to conceal every part of the stem.  The fruit of these vines is incomparably finer than that of any other, either native or exotic, which we have met with n the United States."





What was this 'incomparably finer' grape? Are there specimen closer to home that might provide pollen?

Millardet's Histoire des principales variétés et espèces de vignes d'origine américaine (1885), and Viala's Une Mission Viticole en Amerique (1888) suggest the vines were hybrids of rupestris (rock grape) and riparia (river grape).  This makes some intuitive sense.  Mix a rock grape and a river grape and you get a sand-dune grape.

T.V. Munson disagreed.  He calls the Long expedition grapes 'Longii', for Major Long.  Munson's view seems to have been accepted, though the name got switched to 'acerifolia'.   Munson  pointedly declared in 'Foundations' (1909), "In extended journeys in its native region, the writer has never seen V. rupestris or V. candicans except the latter along its eastern border of distribution. No other species has been seen by me in that large area where it is so abundant, save frequently V. Doaniana." 

A 2013 presentation by Greg,. Klein, Bogler, Jiménez, and Miller tittled." Morphometric analysis of leafvariation in three North American grape species (Vitis acerifolia, V. riparia, and V. rupestris)" seems to take a third view.  Reviewing large collections of specimen, the authors discover there are no morphometric discontinuities.

Does 'no morphometric discontinuities' mean Riparia, Rupestris and Acerifolia are variants on a single species?