Ladysthumb (Lady’s Thumb) or Smartweed Family: Polygonaceae (Buckwheat or Knotweed Family) Genus: Polygonum (some sources use persicaria for the genus) | Species: persicaria, vulgaris, and/or caespitosum (Most common member of this group, at least in the northeastern US, is called Pennsylvania Smartweed – Polygonum Pensylvanicum) Description: Some may also refer to this very common weed