I do NOT live in Texas. (Thank God!) I cannot remember when it ever got to 100.
Small islands: Here we'd use mugo pine, and potentilla a lot.
Larger beds. Larger pine, American elm, spirea, burning bush, cotoneaster, lilac, sea buckthorn, crabapple.
My brother-in-law in Phoenix (a climate that makes Texas look cool and inviting) has a lot of decorative cactus, bougainvilla, yucca, and lots of stone.