I'm an old hand at escaping the desert's midday sun beneath frilly-leafed mesquite trees. Sunday, after reading awhile, I leaned back and saw what's shown below:
Those are mesquite leaves on a spiny, burro-chewed branch. Note the leave's curious configuration. Each leaf is doubly compound, the first division creating two featherlike leaflets atop the petiole, and then each of those leaflets is divided into numerous sub- leaflets, or pinnules. The Y-shaped form with frilly Y-arms is very unusual among tree leaves.
Something about this mesquite tree seemed different from others I've known farther north and farther south. It turns out that our Queretaro mesquites are PROSOPIS LAEVIGATA, sometimes known as Smooth Mesquites. The species so abundant in the US arid Southwest as well as in the Yucatan and southern Mexico is Prosopis juliflora, which has larger, longer leaves. Our P. laevigata seems to be a central-Mexican endemic.
Mesquite, like the abundant and useful Sweet Acacia or Huisache around Jalpan, often is treated as a trash tree. That's a shame because all mesquites are wonderful, not only for the delicious shade they offer at midday. First, they're members of the Bean Family so their roots bear fungus-inhabited nodules (mycorrhiza) that enrich the soil with nitrogen.
Also, mesquite legumes can be dried, ground and used as nutritious flour. A study analyzing mesquite-legume flour found that the "Functional characteristics of whole mesquite pod flour were similar to those of bean flour (Phaseolus vulgaris), and superior to those of whole wheat flour (Triticum sp)." An abstract of that study can be reviewed online here.
But mesquite provides great firewood. You can't beat it for the kind of ranchero-style barbecuing done around here. That's one reason our Prosopis laevigata is on the IUCN's Red List of Threatened Species, as shown at http://www.iucnredlist.org/search/details.php/32939/summ.