Horse herb grows very well under those conditions around my place. The info says it gets to 8 or 10 inches high, but it doesn't get that tall in my dry rocky thin soil conditions. I've got a picture somewhere of it growing wild in the easement in back of our house. Check it out. Nurseries sell it, or you might find some growing wild you could transplant.

Here is a link that might be useful: Calyptocarpus vialis

Here is the picture. Click on photo for larger view:

It might not grow this thickly in a dry year, and other weeds can grow up in it, but if the weeds are pulled before they go to seed you will finally have a pretty thick stand of horse herb only.

I like silver pony'sfoot, SAlvia chionophylum , snakeroot or is it snake plant, and Dalea gregii. These will take abuse. I have rootings avaiolble of most of these.

I bought a plant from Schumachers Hill Country Nursery, that sounds like what your looking for. I think it gets up to 5 or 6 inches tall. I am in the NW part of San Antonio, close to the Medical Center. Email me if you would like to come by and get a start. I do not remember the name of the plant, but I think it is pretty, and has color. I think they may still sell it, I am not sure, I have not been back to Schumacher's since last April, after the Buda plant swap. Barbra