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Adapted from Jim Conrad's online book A Birding Trip through Mexico, This excerpt from "The Cactus Desert at Zapotitlán" in southeastern Puebla state
AN ECOLOGICAL ISLAND
The Zapotitlán desert is an ecological island in the sense that it is completely surrounded by non-desert biological communities. It occupies only a small section of the southeastern corner of Puebla State, and the northwestern corner of Oaxaca State. It owes its presence to the fact that right across the Tehuacán Valley to the east, the Eastern Sierra Madres rise high enough to block prevailing winds carrying moisture off the Gulf.
Similar to many oceanic islands, its inhabitants are often strange and unique. One of the most eye-catching is the Mexican Poneytail, Beaucarnea gracilis, shown at the right. Poneytails are sold as succulents in many North American garden shops, but the one sketched here has a trunk big as a full-sized refrigerator.
Botanist C.E. Smith Jr. writes that some 29 percent of the plant species found here are endemic -- found nowhere else on Earth. In fact, there are several endemic genera here. Some of those genus names look and sound wonderfully exotic: Oaxacania, Pringleochloa, Setchellanthus, Solisia...