Can you help me identify this wildflower?

I came across a wildflower at the Trinity River Audubon Center that I cannot identify.  I thought I would draw on the collective expertise of the folks who read this blog.  If you have any idea what this plant is, please let me know in the comment section.  Many thanks in advance.

Trinity River Audubon Center, 6500 Great Trinity Forest Boulevard, Dallas, TX 75217, USA
street address:	6500 Great Trinity Forest Boulevard
ZIP/postal code:	75217
neighborhood:	Trinity River Audubon Center
city:	Dallas
state/province:	TX
country:	USA
latitude, longitude:	32.7124233, -96.7088488 32.7124233 -96.7088488 N32° 42.7454', W096° 42.5309' (precision: feature/building)

http://www.gpsvisualizer.com/geocode


It is obviously a composite flower with a raised disk.





 

This is a very large image of the entire plant showing the stems and leaves.  Notice the keels on the stems.  The plant stands about a meter high.
 

Let me know what you think and many thanks in advance.


M. Gans
Eastfield College
Mesquite, TX