Ecoregion Definition: Distribution of Type-defining Plants

According to all of our authorities, the defining plants of our Arizona Uplands Series of the Sonoran Desert are primarily the Saguaro columnar cactus and the Foothills (Green) Palo Verde. Zimmerman's (1969) map of plant distributions (which corresponds well with our own observations, so far as these go) places both types reaching well to the south and east of Cascabel (shown just right of upper-center in the portion of Zimmerman's map presented below). (Zimmerman's map shows Saguaro distribution running south even beyond the Narrows on the West side of the San Pedro River, a pattern we have not yet observed.) In contrast, the plants generally regarded as type-specimens of the Chihuahuan Desert include the Tarbush and Sandpaper Bush, but neither of these occur in the vicinity of Cascabel. Zimmerman shows the northern limits of Tarbush to be well south of the Narrows, just north of Tres Alamos Wash. Sandpaperbush extends northward on the edge of the Little Rincon Mountains west of Kelsey Canyon Wash and Teran Wash (and further northwest near Soza Canyon Wash and Buehman Canyon Wash, but it is not placed in our area (and we have seen neither of these plants in our area around Cascabel).