Ask Mr. Smarty Plants

There are several pines native to Texas, but most of them seem to occur either in far East Texas or far West Texas. What you have may be none of the natives or a hybrid; it doesn't matter too much as members of the pinus genus share several characteristics that may be affecting what will grow around the tree.

We were unclear if you were trying to plant around the tree or beneath the tree. We're assuming that if the tree is doing well, that would probably mean that you have acidic soil, which pines all need. They even contribute to the acidity of the soil with their fallen needles. As the needles decompose, they add still more acidity to the soil. If you are trying to grow plants around the tree, they would just need to be adaptable to the acidic soil and part shade. If you are trying to grow plants beneath the tree, they are having to deal with the heavy shade of the pine, plus the needles on the ground.  We would recommend that you let the pine needles stay beneath the pine, they make a good mulch, should inhibit any weeds from coming up, and will continue to contribute to the health of the tree, itself.

If you really want to plant something beneath the tree, you will have to consider those pine needles and their acidity. As we said, the needles will suppress weeds, but they probably also will suppress anything else you try to put in there. We would not recommend Ophiopogon japonicus, dwarf mondo grass, as it is a non-native to North America from China, Korea and the Philippines. Phyla nodiflora (turkey tangle fogfruit), which you mentioned, and Dichondra argentea (silver ponysfoot) are both possibilities for a sun or part shade ground cover. 

Phyla nodiflora

Phyla nodiflora

Dichondra argentea

Dichondra argentea