I've found several of these little plants in my yard. They have little white flowers that turn to small green berries that turn dark purple when ripe. I burst open one of the ripe berries and found it has several little white seeds on the inside. The leaves are unlobed and seem to be a popular source of food for insects (holey).
Some of the plants seem to be growing somewhat upright, while others are more prostrate.
What proof is there that Solanum americanum will mess up your tomato crop?
It is wise to be cautious about the toxicity of wild plants, but it is better to learn about the plants in your area and understand them, rather than carry a paranoia around with you to spread to others.
Most plants in the Nightshade Family, Solanaceae, have toxic parts, but we still eat them. This includes Tomatoes, Potatoes, Eggplants, Tomatillos, Chili Peppers, Sweet Peppers, Tree Tomatoes, Naranhia, etc.
Every plant that we eat, has parts that are not usable for food. Most folks eat Apples and other fruit of the Rosaceae, while avoiding the cyanide containing leaves of the plants. People chew down the leaves of lettuce, but are wise enough not to try and eat lettuce roots which are not easy to digest.
If one learns about the plants and nature that exists around them, they don't have to be afraid of the natural world that occurs there.