Ask Mr. Smarty Plants

So far, there is no single, comprehensive source focusing on the edible plants of only the Texas Hill Country. Those of us interested in this topic usually rely on Delena Tull's Edible and Useful Plants of Texas and the Southwest and then figure out which plants occur in central Texas using sources like Correll and Johnston's Manual of the Vascular Plants of Texas and the USDA Plants database, the latter of which allows you to determine what counties a species occurs in.

There is also a Texas archaeology website organized by region, called Texas Beyond History, that contains ethnobotany information. If you go to their page and click on "Plateaus and Canyonlands" and then on "Nature's Harvest", an array of plants known to have been used by the area's inhabitants will come up and you can then click on each plant to learn if it was eaten. I would recommend going through each region, since many of the species featured for other regions extend into central Texas.

You can also glean what you can about the topic from a couple of regional history books that touch on post-Columbian plant usage by indigenous peoples: The Native Americans of the Texas Edwards Plateau, 1582-1799 by Maria F. Wade and Spanish Expeditions into Texas 1689-1768 by William C. Foster. The latter in particular has a good appendix on possible identities of plants mentioned in historic records, with assistance from Scooter Cheatham and Lynn Marshall of the Useful Wild Plants of Texas volumes, another good source of information. You can also use Daniel Moerman's excellent, comprehensive Native American Ethnobotany, but that's continent-wide so you'd have to limit your focus to only regional plants.

For an earlier attempt we made at providing an introductory list of edible plants of central Texas, see this answer to a previous Mr. Smarty Plants question.