herbal tea vs tea plant

herbal tea

noun
  • A beverage made by infusing the leaves of various herbs, generally not including true tea (Camellia sinensis). 

tea plant

noun
  • The bush Camellia sinensis, the leaves of which are picked, dried and used to make the beverage tea. 

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