As Eastern viticulture reemerged after Prohibition in the late 1960s, Norton and Cynthiana were mixed in vineyards and officially deemed as synonymous. -- Lucie Morton
With the return of the Norton and Cynthiana grapes post-prohibition in Missouri, Virginia, Arkansas (courtesy of Stone Hill Winery in Missouri, Horton Vineyards in Virginia, and Post Familie Vineyards in Arkansas) the common perception was that the two grapes were either clones or synonyms. Modern genetic data based on single nucleotide polymorphisms (SNP’s) could not distinguish Norton from Cynthiana as a phylogenetic tree constructed based on 1.2 million SNP’s could not differentiate Norton from Cynthiana. 
Yet, independent viticulturist Lucie Morton strongly disagrees that they are the same cultivar and by using Ampelography -- the study of a grape in terms of its historical record and physical characteristics in terms of leaf, cluster, berry and seed shape -- she asserts that the two grape varieties are completely different cultivars. At the 2025 Eastern Winery Exposition she presented this hypothesis through an analysis she conducted with Dean Volenberg (viticulture and winery operations specialist at the University of Missouri) and Diego Berrios Galaz - winemaker at Virginia's Casanel Vineyards. The results are also available in the March 2025 edition of Wine Business Monthly. I sure wish this presentation or the companion article were available before my Norton seminar at the February BevFluence Chicago Speakeasy. The rest of this post merges information from the presentation and the Grape Sleuthing Through History WBM article. 
The Norton grape was born in the vineyard of Dr. Daniel Norton around 1820 when he tried to pollinate the Bland grape with a Pinot Meunier. Instead a free-living V. aestivalis replaced the Burgundian grape as the pollinator. Since the Bland and the V. aestivalis gapes had some labrusca and vinifera in their DNA, the Norton grape is comprised of various percentages of V. labrusca, V. vinifera, and V. aestivalis.
Cynthiana was long thought to have originated in Arkansas, but Morton researched historical records that pinpoint the grapes origination in Red River, Ohio in the 1840s. At that time, Ohio was perhaps the leading grape growing region in the United States. The famed Prince Nursery in Flushing Long Island listed a variety called Red River in 1844 and in its 1858 catalogue changed the name to Cynthiana (Syn Red River). The Arkansas wine industry did not really take off until the 1870s. (Norton had been included in the Prince Nursery catalogue since 1822).
In Missouri, George Hussmann (considered a father of the Missouri wine industry) received cuttings of both Norton and Cynthiana and in 1859 wrote, "The Cynthiana (Red River) originated in Ohio; in appearance it is very much like the former (Norton); makes, however a wine of a lighter color..." And "U.P. Hedrick opined in The Grapes of New York (1908) that Norton and Cynthiana must be considered as distinct varieties." Thus, up until prohibition they were considered two separate grape varieties.
What are the ampelographic differences between Norton and Cynthiana? The Norton leaf can resemble a "bat wing" through its lateral lobes and is longer than wider, thinner leaf veins, with triangular teeth. The Cynthiana leaf resembles a "spade-bit" through its lateral lobes and is wider than long, thicker leaf veins and round-based arches with tips for teeth. Its clusters contain larger and longer berries than Norton's and its smaller greener seeds cling to the pulp. Whereas with Norton, the seeds are larger and redder and do not cling to the pulp. See the companion image, but the last notable difference is that the dormant buds for Cynthiana are little triangles pointed to conical, whereas for Norton, they have a rounder base often compressed, obtuse to conical.
