Potatoes, Nightshades and Tomatoes
From researching, I gather that the tomato is a species of plant in the potato family and the nightshade genus. See USDA link below. I know all over the internet people claim the tomato is in the nightshade family, but from the USDA link below, that is not correct - it is in the potato family and the nightshade genus.
Here is a link that might be useful: USDA Solanum Lycopersicum Reference