Persicaria spp.; smartweed, knotweed [Polygonaceae]  Several species of weedy annual or perennial plants.  Small flowers with 5 white to pink petals or petal-like sepals, growing in spikes or spikelike branches, or in the leaf axils.  The stems are jointed, with a membranous sheath above each joint.  The various Wisconsin Persicaria species may be erect, sprawling or trailing plants, and are common in moist or wet open places.  Some species are native, others introduced.  Flowers in summer and early fall.  [103]