There's no way to give an exact ID with these photos. Can you isolate the plant in question, and just photograph it alone, instead of the way it is now, being tangled in a rat's nest of who knows what. I'm assuming the white flowers in the 1st photo are another genus, maybe Clematis. They don't match any Mirabilis species native to Texas. Most of the native Mirabilis have similar tepals, so that's not a good method of telling them apart. I'm thinking the whole grenade protruding from the tepals is the seed, mainly based on my experience with Mirabilis jalapa.

OK, so I believe it might be Mirabilis albida (Pale Umbrella Wort)...although I'm still not sure which part is the actual seed(s)?

The seed is circled. The darker part at the tip might fall off and thenthe green 'grenade' would be the seed. Pictures of albida show the seeds without that part at the tip, so maybe the tip is just part of the flower, and will fall off. I looked at some Texas Mirabilis species at google photos, and they don't always show what the seeds look like. What makes you think it's albida?