I only saw a few clusters of this low shrublet on the sandy roadside of FM 2644 about 3.3 mi W of Carrizo Springs, in western Dimmit Co., TX. Not being familiar with any of the native "birds-of-paradise" or "rush-peas", it took me some time to sort through them (including the shifting genera), but in the end, I matched this to Caesalpinia caudata--certainly a Life Plant for me and one of the best finds of my visit. Note the typical leaf (2nd image) with about 5 main subdivisions (pinnae), the terminal one of which is much longer than the side ones. The stems, peduncles, pedicels, calyces, and petals are all dotted with red glandular hairs.

This is a locally occurring plant in the SW part of Texas and adjacent Mexico:
http://bonap.net/MapGallery/County/Caesalpinia%20caudata.png
@bethower's record of the species in adjacent Nuevo Leon seems to be the only other image of a living example of this species:
http://www.inaturalist.org/observations/480003
There are a few dozen images of pressed specimens at U.T.'s Plant Resource Center:
http://prc-symbiota.tacc.utexas.edu/taxa/index.php?taxon=4775

The PLANTS and ITIS databases use the curious common name of "tailed nicker":
http://plants.usda.gov/core/profile?symbol=CACA26
http://www.itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=26502