The plant is a black cherry Prunus serotina, a weedy little tree found throughout the New World. The leaf bears the mushroom-like galls of a tiny arachnid, the mite Eriophyes cerasicrumena. The animals are living inside the protuberance.
The white discoloration patterns on the leaf are feeding marks left by leafhoppers--small (but enormous compared to the mites) insects that puncture the leaf and feed on the fluid within.
Thanks always to Charley Eiseman, who expertly divines animals from the marks they make on plants. He rears galls to identify the adult insects--I think he has discovered new or locally unknown species doing this.