These trees can be identified from their alternate, complex leaves with 12-18 leaflets, each 3-5 inches, and round 2-3 inch fruit with greenish-yellow husks. The fruit of Black Walnuts leach a chemical called juglone that inhibits the growth of other plant species so these trees, common to moist uplands and floodplains, are usually characterized by having a ring of ground barren of all other plants surrounding them.