We don't have synonyms for jointweed yet — it may be a rare, specialized, newly coined, or misspelled word. The closest thesaurus entries we have are jointed and jointured.
(n) :
Any member of the genus Polygonella, now included in genus Polygonum of knotweeds and smartweeds, especially Polygonella articulata, now Polygonum articulatum.
(n) :
Any member of the genus Polygonella, now included in genus Polygonum of knotweeds and smartweeds, especially Polygonella articulata, now Polygonum articulatum.