cockspur vs watergrass

cockspur

noun
  • A kind of grass (Echinochloa crus-galli). 

  • A blade for tying to the foot of a gamecock. 

  • A kind of hawthorn (Crataegus crus-galli). 

watergrass

noun
  • Any of various grasses in the genus Echinochloa that are capable of growing in water. 

  • Bulbostylis barbata, an Australian sedge that grows near water. 

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