Amsonia longiflora (Trumpet Slimpod), Travis County, Texas, found 29 March 2005.
All photos Copyright 2005 by Scott Haywood.

A. longiflora has a longer corolla tube than Amsonia ciliata var. texana.  Amsonias are often blue, or at least tinged blue, but these were white.  More on the genus Amsonia can be found in Shinners' & Mahler's Illustrated Flora of North Central Texas.