Plants are known to be cold hardy to at least -10°F.
Desert globemallow is one of those native plants that keeps on giving, asking so little in return and is a worthy addition to any native or xeric garden. Typically, desert globemallow sports pretty pink flowers. though some plants will bloom white, coral or lavender. Whatever color, they are worth the addition to your sunny and dry landscape for their pleasant cheery nature. Similar to appearane to S. coccinea, a coral blooming species.
Not all succulents are cacti, nearly all cacti are succulents (a few exceptions). Nearly all cactus species are native to the Americas, providing a prickly evergreen presence. There are many cactus that are cold hardy for the Texas Panhandle. There might be one for your garden.
Bigelow's tansyaster is easy to confuse with Tahoka daisy but is not as showy. Bigelow's aster is a fall blooming biennial, with far fewer purple rays and a smaller, yellow brown center disk. It populates plains in Colorado, Arizona and New Mexico. In the fall, whole fields will wear a purple haze due to this tansyaster.
Prairie dropseed is smaller than both alkali or giant sacaton, more fitting for the city garden. A warm season bunch grass, prairie dropseed is a most attractive low or medium water-use grass with graceful green foliage. The seed heads emerge in late summer into fall with light pink seeds, that is said to naturalize some, but not invasively. A slow grower. Foliage turns a pleasing golden orange in the fall. Native throughout the Great Plains, including Texas. Tolerates most soil conditions.
Littleleaf mockorange is native throughout the foothills, dry rocky slopes and open woodlands from 4000 to 8000' in the Southwest usually growing to only 4 feet. This native mockorange is similar in form to the European import, they are fragrant, but not of orange. Attractive white, 4 petaled flowers bloom in early summer, small slightly glossy green leaves. Coldy hardy, heat and drought tolerant.