Excerpts from Jim Conrad's
from the September 28, 2007 Newsletter issued from Sierra Gorda Biosphere Reserve, QUERÉTARO, MÉXICO
The common Mesquite mantling vast acreages of arid northern Mexico is PROSOPIS JULIFLOR,. shown below:
In that picture I'm holding the petiole of a single compound leaf. Atop the petiole two leaflets arise, and each leaflet is divided into many pinnae.
You might be interested in comparing these leaflets with those of the "Smooth Mesquite," P. laevigata, we saw in Querétaro, which you can see here. They share identical basic structure, but the relative sizes and general "feeling" of them is very different.