Complex sentence: It occurs naturally in the leaves, roots, husks, and bark of plants in the Juglandaceae family, particularly the black walnut, and is toxic or growth-stunting to many types of plants.
Split into simpler sentences: It occurs naturally in the leaves, roots, husks, and bark of plants in the Juglandaceae family, particularly the black walnut. In the case of juglone, it is toxic or growth-stunting to many types of plants.