A Palo Verde tree grows above an Engelmann's Prickly Pear (Opuntia engelmannii) and a Saguaro (Carnegiea gigantea). The Palo Verde may have served as a nurse plant for the young Saguaro. These trees protect Saguaro seeds from foragers and also provide shade for the juvenile plant.

Location: East Section, Saguaro National Park, Tucson, AZ.

1997