sagebrush vs southernwood

sagebrush

noun
  • Any of several North American aromatic shrubs of the genus Artemisia, having silvery-grey, green leaves. 

southernwood

noun
  • An aromatic shrub, Artemisia abrotanum, related to wormwood. 

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