The nopal cactus is the prickly pear cactus on which the eagle stands. It is a very recognizable plant in Mexico and is deeply associated with the landscape, food, and identity of the country. In the coat of arms, it is also a key part of the founding sign shown to the Mexica.

In the legend, the eagle appears on a nopal growing from a small island in Lake Texcoco. Seeing that sign meant the Mexica had found the place to build Tenochtitlan. The nopal therefore represents both the land itself and the legendary origin of the capital.