knotgrass vs lamb's quarters

knotgrass

noun
  • An annual plant, Polygonum aviculare, found in fields and wasteland 

  • Paspalum distichum, a weedy perennial grass of wet areas 

lamb's quarters

noun
  • Any of several similar plants of genera Chenopodium and Atriplex. 

  • Chenopodium album, of the goosefoot family, sometimes used as a potherb 

How often have the words knotgrass and lamb's quarters occurred in a corpus of books? (source: Google Ngram Viewer )