From the Super Mario Wiki
The Painting is an item in the PC release of Mario's Time Machine. It was painted by George Washington Carver and features some flowers. Mario receives it from one of Carver's students after traveling back in time to Tuskegee circa 1915. While the two of them are talking, the student brings up the usefulness of certain plants, then gives him the Painting to demonstrate some of those plants, as well as helping her study by giving her some Ice Cream. Meanwhile, Booker T. Washington tells Mario that he wanted to show him that very same painting, as it shows "the connection of soil, plants, animals and humans," and he excuses himself to go look for it. Mario promptly gives the Painting to him, and he excitedly begins to talk about Carver's studies with agriculture.