horseweed vs indigo bunting

horseweed

noun
  • A plant of the species Cichorium intybus 

  • Any of various flowering plants of the genus Conyza. 

indigo bunting

noun
  • A blue bunting of North America, Passerina cyanea. 

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