helianthus vs sunflower

helianthus

noun
  • Any plant, of the genus Helianthus, having large flower heads with dark disk florets and showy yellow rays; the sunflowers 

sunflower

noun
  • Any plant of the genus Helianthus, so called probably from the form and color of its floral head, having the form of a large disk surrounded by yellow ray flowers. 

  • Any flat, radially symmetric organic compound such as coronene 

  • A bright yellow, like that of the flower petals. 

  • The commonly cultivated species, Helianthus annuus, a native of America. 

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