lignum rhodium vs rhodium wood

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). 

rhodium wood

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