It’s called Ditch Stonecrop (Penthorum sedoides), and its listed in Peterson’s Field Guide to Medicinal Plants and Herbs:
American Indians used seeds in cough syrups. Historically, plant tincture was used as demulcent, laxative, and tonic, for mucous membrane irritations, vaginitis, diarrhea, dysentery, pharyngitis, tonsillitis, piles, chronic bronchitis, and nervous indigestion.
Wow. That’s a lot of stuff. The flowers are supposed to be “white to greenish” but my closeups all had a pink tint:
It can be found throughout the east, and in the northwest in wetlands. Indeed, it is listed by the USDA Plants database as an obligate species for wetlands. So, next time you’re out hiking through muck, keep your eyes open for Ditch Stonecrop!