fleabane vs horseweed

fleabane

noun
  • Conyza spp. (butterweeds or horseweed) 

  • Pulicaria spp. (false fleabane), especially common fleabane (Pulicaria dysenterica subsp. dysenterica, formerly Inula dysenterica) 

  • Erigeron spp., especially Erigeron acre (blue fleabane) 

  • Inula spp. (yellowheads) 

  • Also, in subfamily Cichorioideae, Vernonia spp. (ironweeds). 

  • mostly in two tribes of subfamily Asteroideae 

  • Pluchea spp. (camphorweeds) 

horseweed

noun
  • Any of various flowering plants of the genus Conyza. 

  • A plant of the species Cichorium intybus 

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