thousand-leaf vs water milfoil

thousand-leaf

noun
  • Achillea millefolium or common yarrow, a flowering plant widespread in the temperate Northern Hemisphere, featuring finely divided leaves. 

water milfoil

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

How often have the words thousand-leaf and water milfoil occurred in a corpus of books? (source: Google Ngram Viewer )