[1] The Zacatonal consists of several enclaves of grassland and shrubland occupying the highest peaks of the Trans-Mexican Volcanic Belt, covering about 306 square kilometers (118 sq mi).

Other grasses and forbs include Arenaria bryoides, Descurainia impatiens, Draba jorullensis, Lupinus montanus, Muhlenbergia pusilla, M. quadridentata, Oxalis sp., Pedicularis orizabae, Penstemon gentianoides, Poa annua, Potentilla staminea, Sicyos parviflorus, and Trisetum spicatum.

Other alpine zone plants include Festuca tolucensis and species of Carex, Cerastium, Cirsium, Draba, Eryngium, Gnaphalium, Lupinus, Luzula, Oxylobus, Phacelia, Plantago, Potentilla, Ranunculus, and Senecio, together with ferns, mosses, and lichens.

[2] The Sierra Madre sparrow (Xenospiza baileyi) is found in the transition zone between the Zacatonal and pine forests.

In 1935 the Mexican government placed nearly 4,000 km2 of the mountains surrounding the Valley of Mexico under protection, including both Zacatonal and lower-elevation pine-oak forests.