The nightshade species of North America consist of black nightshade (Solanum nigrum L.), American black nightshade (Solanum americanum Mill.), hairy nightshade (Solanum surrachoides Sendt.) and eastern black nightshade (Solanum ptycanthum Dun.). Eastern black nightshade is a problem weed in many soybean producing areas and is the predominant problem nightshade in Kentucky. In addition to field crops, the nightshades are also problem weeds in canning peas (Pisum sativum L.), field beans (Phaseolus vulgaris L.), potatoes (Solanum tuberosum L.) and tomatoes (Lycopersicon esculentum Mill.). Previously, most nightshades in Kentucky have been referred to as black nightshade. It is now known that black nightshade occurs in the U.S. only in the western states, while eastern black. nightshade is commonly found in many states east of the Rocky Mountains. These species are similar in their gross morphology and are easily confused with each other. When grown under different environmental conditions, the nightshades may vary considerably in many taxonomic characteristics frequently used for identification and make identification more difficult (Ogg, A.G., B.p. Rogers and E.S. Schilling, 1981).
Rodrigue, L. G.; Witt, W. W.; Slack, Charles H.; and Martin, J. R., "Eastern Black Nightshade" (1982). Agronomy Notes. 85.