Summer grape is a vigorous vine climbing to a height of 35 feet by means of tendrils, or sprawling over low bushes and trees.
Leaves are alternate, simple, 2–8 inches long and wide, heart-shaped or egg-shaped to round; margins of some irregularly toothed and unlobed, some leaves with margins shallowly to deeply 3- to 5-lobed, lobe sinuses (cleft between two lobes) narrow and rounded, base heart-shaped; upper surface yellowish green with a few hairs on the veins; lower surface whitish, with light rusty, cobwebby hairs.
Stems are reddish brown, finely ridged, woolly at first but soon smooth; small branches are round in cross-section, not angled; tendril emerges opposite the leaf. Bark on branches shreds early; bark on older stems brown with long, papery shreds. Wood is tough, porous, pale brown, with a large pith.
Flowering is in May–June. Flowers are green, minute; male and female flowers in separate clusters on same plant; petals 5, dropping early. Clusters are ½–3 inches long; cluster stalk 2–6 inches long.
Fruit matures in July–October. Fruit dark blue to black globe-shaped berries, ¼–½ inch thick, with a thin whitish coating, sweet, juicy, in clusters 3–5 inches long. Seeds 2–4 per fruit.
Habitat and Conservation
This species, in its ‘Norton’ hybrid/cultivar form, is the official grape of the state of Missouri. The genetically identical ‘Cynthiana’ is the state grape of Arkansas. Producing a dry, “big” red wine with complex flavors, Norton is the cornerstone of the Missouri wine industry. Grape growers and winemakers in Hermann were using it in the 1840s and ’50s. Before Prohibition interrupted development of Norton, wine critics were hailing it as a serious rival to Cabernet, Pinot Noir, Merlot, and so on. It is probably the oldest native American grape variety used for commercial wine production.
This is one of the native grape species that was used extensively in rescuing European wine grape varieties in the late 1800s, after a New World root louse was accidentally imported to Europe. This aphidlike insect pest ravaged European vineyards, threatening to destroy the wine industry centered on Cabernet, Zinfandel, Riesling, Chardonnay, and many other famous varieties; fortunately, people figured out that New World grapes were naturally resistant to the pest, so Old World vines were grafted onto New World rootstocks.
The fruit is eaten by many species of birds and mammals, including cardinal, cowbird, bobwhite, ruffed grouse, wild turkey, raccoon, red fox, and deer.
The foliage is browsed by deer, and the tendrils are eaten by wild turkey.
The catbird, mockingbird, brown thrasher, and cardinal use the long strips of bark in the middle layer of their nests.
Several species of sphinx moths use wild grape species as larval food plants.