mugwort vs southernwood

mugwort

noun
  • Any of several aromatic plants of the genus Artemisia native to Europe and Asia. 

  • Artemisia vulgaris, traditionally used medicinally. 

southernwood

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

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