devil's nettle vs water milfoil

devil's nettle

noun
  • Achillea millefolium or common yarrow, a flowering plant native to temperate regions of the Northern Hemisphere. 

  • Dendrocnide sinuata (synonym: Laportea crenulata), a species of nettle in the family Urticaceae found in Australia and South Asia. 

water milfoil

noun
  • Any of several submerged aquatic plants of the genus Myriophyllum. 

How often have the words devil's nettle and water milfoil occurred in a corpus of books? (source: Google Ngram Viewer )