lemon verbena vs verbena

lemon verbena

noun
  • A deciduous perennial shrub native to South America, used for its lemon-like fragrance and flavor, Aloysia citrodora. 

verbena

noun
  • Verbena, a genus of herbaceous plants of which several species are extensively cultivated for the great beauty of their flowers; vervain. 

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