Siberian Elm

Siberian Elm. Ulmus pumila.  Asian-origin invasive. Wretched.  Fast growing. Wind-dispersed seeds.  Often accidentally grown to maturity, though the wood is weak and the tree is short-lived in Chicago.

The bottom picture shows a 1-inch tall plant I pulled, with a 6+ inch root that was growing under a wall.

Look for it in neglected spaces and everywhere.