Favoritos de tsimmonds

This seems to fit...Growing near the river bank in sandy soil, full sun.
Key breaks (FNCT):
Leaves glabrous on upper surface (photo 9)
Bracts broad, not linear (photo 9)
Pores near the middle (photo 5 and 6)
Pore narrowly oblong, <0.5mm wide and cartilage with narrow scarious margins (photo 6) = T. holzingeri
From description (Vascular Plants of Texas):
Lower stem hairy (photo 11), upper stem scabrous (photo 10). Capsule pores sunken, narrow, in the middle of the capsule. "Seeds lustrous, lenticular, 0.4-0.7mm long, minutely low-tuberculate in longitudinal lines" (photos 7 and 8)

After seeing @alan_rockefeller's observation HERE I had to go take a look!

Photos:
1&2 - Upright, multiflowered, calyx lobes 5
3 - Basal leaf narrow (oblong-lanceolate?) not clasping
4 - Middle part of stem shows calyx lobes 3, leaves smaller
5 - branching
6 - top of leaf glabrous
7 - bottom of leaf glabrous
8 - fruiting capsule long and narrow, fracturing near apex
9 - roots (not diagnostic)
10 - Measurement of inflorescence
11 - Seeds
12 - Seeds

I agree with @sambiology on his observation HERE that this keys out as T. leptocarpa using FNCT.

Exciting find Alan!!