The term “muscadine” is commonly used to refer to either wild V. rotundifolia or commercially-used cultivars, the latter of which form the subgenus Muscadinia.
The most distinct genetic difference between table grapes and muscadines is the number of somatic chromosomes: Muscadinia species have 40 (2 ×= 2n = 40), while Vitis species have 38 (2 ×= 2n = 38). Therefore, Muscadinia and Vitis are not compatible to breed together!
(While Vitis species can hybridize freely, Vitis × Muscadinia hybrids are rare and normally sterile as a result of having 39 chromosomes.)
Muscadine also has three distinct floral types, while most flowering plants only have one or two. There’s perfect hermaphrodite, staminate (male), and imperfect hermaphrodite (female). Male flowers can self-pollinate female ones, while perfect hermaphrodites are self-fertile and only rarely observed in the wild.
There might be a reason for having extra chromosomes. According to a 2019 article in the Journal of Agriculture, 
“muscadines resiliency in productivity and disease tolerance in the southeastern U.S. coastal plains is suggestive of evolution on sandy to sandy loam soils with extreme disease and pest pressure, and intense heat and humidity.”