elecampane vs sweet flag

elecampane

noun
  • A tall Eurasian herb, Inula helenium, whose roots have been used medicinally. 

sweet flag

noun
  • A perennial wetland plant, Acorus calamus, with an aromatic medicinal root, formerly used to strew floors. 

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