These appear to be the first photos of the tiny cobweb weaver Theridion llano, a Texas native. The spider has a body length of 1.5mm. It crawled out of a dried monarda seed head.
I owe thanks to Laura P. and Chad Heins on BugGuide for helping me to identify this, as well as to Allen Dean for confirming the identification. Here is the BugGuide entry for this spider.