Latin names: Glandularia bipinnatifida
Spanish name (much prettier!): moradilla (little purple one)
Other common names: Dakota mock vervain
There is not a lot of information on the internet about this plant. No legends or associations with famous historical characters. But if you want more details, you can go to these websites:
Lady Bird Johnson page
Uvalde office of Texas AgriLife Extension page
This plant does not appear in Toxic Plants of Texas.