knotweed vs polygonum

knotweed

noun
  • Any of several plants of the genus Polygonum, with jointed stems and inconspicuous flowers 

polygonum

noun
  • Any of many plants, of the family Polygonaceae, embracing a large number of species, including bistort, knotweed, smartweed, etc. 

How often have the words knotweed and polygonum occurred in a corpus of books? (source: Google Ngram Viewer )