PlantFiles: Graybark Grape, Summer Grape
Vitis cinerea

After much research, I've concluded this is the grape that is so widespread in my area. Texas has 13 or 14 varieties of native grapes and the rootstock of some (including sand grape) were used to cure the phylloxera plague in 19th century Europe, where most of the vineyards were destroyed. Native Texas grapes are resistant. Without those native Texas rootstock, there would be no V. vinifera wine industry in Europe today. From what I've read elsewhere, it's more commonly called "winter grape" than "summer grape" as on this site. This is supposedly because the fruit ripens more toward winter. They have been ripening here for at least the last month and there are many freshly ripened ones still on the vines and it's now mid October. I also read elsewhere that you can see "spider webs" on the back of the leaf under slight magnification and I did find this on the leaves. I'll be uploading pics. The grapes are the size of a sweet pea, sometimes slightly larger and the taste is mildly tart and semi-sweet and not much juice. There are one to three seeds per grape.