Ask Mr. Smarty Plants

On the Texas Invasives website, we found this page on Lantana montividensis which may prove to be the one you are finding on your land. It is a native of tropical South America and is widely used as a ground cover. The very fact that it is on the Texas Invasives list is an indication it's probably not the most desirable plant.

However, there is Glandularia bipinnatifida (Dakota mock vervain) which also has clusters of lantana-like purple flowers. This is a native of Texas, can spread to cover acres with its trailing branches and flowers, and is deer-resistant. Because your land is previously uninhabited, it is more likely that the plant in question is this one. Whether you try to keep it or remove it depends on the uses you wish to make of the land. It attracts butterflies, and blooms a good part of the year, has no poisonous parts and is adapted to the area, so it would make a very attractive addition. If you're planning a more formal garden for the property, the Dakota mock vervain could itself become invasive. Even a native can be invasive. 

If neither of these appear to be the plant in question, you might try sending us a picture, using the instructions on the  "Ask Mr. Smarty Plants" page in the lower right hand corner, and we'll see if we can get a better identification.

Glandularia bipinnatifida