lignum rhodium vs rose root

lignum rhodium

noun
  • Rhodiola rosea (Crassulaceae). 

  • An oil yielded by such plants, used in herbal medicine. 

  • The fragrant wood of several shrubs and trees, especially of species Convolvulus scoparius and Convolvulus floridus (Convolvulaceae) from the Canary Islands, and of the West Indian Amyris balsamifera (Rutaceae). 

rose root

How often have the words lignum rhodium and rose root occurred in a corpus of books? (source: Google Ngram Viewer )