oriental lady's-thumb smartweed

oriental lady's-thumb smartweed, also called cespitose smartweed, bristly knotweed, and long-bristled smartweed, also has latin synonyms! Polygonum caespitosum is the one used in some of the books i have. i believe persicaria longiseta is more recent/correct.
visually very very similar to lady's thumb, Persicaria maculosa, this smartweed can be distinguished from it by its lack of leaf spots! lady's thumb has odd dark splotches in the middle of its leaves, which these do not. this particular smartweed also has long hairy bristles on the "sheathing stipule," a trait unique to it (hence the "long-bristled" name), which is nigh impossible to photograph with my phone camera.
considered invasive in our neighboring new hampshire, smartweed is native to asia and occurs there as a weed in, among other places, rice paddies. like many weeds i've seen, it grows in roadsides and other disturbed land; however, this one prefers moist soil and can be found in wetlands and floodplains and other wet areas.

oriental lady's-thumb smartweed blooms from june to october.