Texas vervain, Verbena halei

No, not the Verbena. Wrong leaves, wrong flowers. No idea what it is specifically but it does look like a Lythrum. L alatum perhaps?

There is a resemblance to Verbena halei, and the flowers look similar, but the OP's photo is blurred. A clearer photo of the flower showing the pedicel would help, but the flower stalk in your photo gardengal is made up entirely of flower buds, while the stalk in the OP's photo contains new leaves yet to unfold, and the leaves of Verbena halei are typical lobed Verbena leaves, while the OP's plant has leaves that are entire.

The closest match I've found so far is Epilobium leptophyllum, but I'm not sure about the flowers or pedicel lengths, but the rest seems to fit.

Lythrum alatum I think, floral had it.

OP’s plant has six regularly spaced petals, not five in a two top, two side, one bottom arrangement. Very different from Verbena when enlarged.

Here's a closer-up view of the flowers. I also went back to look for any basal leaves (V. halei should have dissected leaves), and found none - this plant arises as a bare stalk from the ground, and the linear leaves in the first photo are the only kind present. I'll look more carefully at Lythrum alatum.

My flowers look quite similar to those at https://www.wildflower.org/gallery/result.php?id_image=30934 , so I think L. alatum is likely correct. I can't find photos that have such crinkly petals as mine, but I'm inclined to attribute that to a variation in my particular specimen.

Update. This is Lythrum lanceolatum, (Weakley). Formerly Lythrum alatum var. lanceolatum, and Lythrum subsp. lanceolatum