lignum rhodium vs roseroot

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). 

roseroot

noun
  • Rhodiola rosea, a perennial crassulaceous plant with many claimed health benefits that grows in cold regions. 

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