amaranthus vs knotgrass

amaranthus

noun
  • Any of the genus Amaranthus; an amaranth. 

knotgrass

noun
  • Paspalum distichum, a weedy perennial grass of wet areas 

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

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