selfheal vs valerian

selfheal

noun
  • A small, herbaceous European plant with blue-violet flowers from any species of genus Prunella. 

  • Especially, Prunella vulgaris. 

valerian

noun
  • A hardy perennial flowering plant, Valeriana officinalis, with heads of sweetly scented pink or white flowers. 

  • An extract of the dried roots of the Valeriana officinalis used in herbal medicine as a sedative. 

  • More generally, any plant of the genus Valeriana. 

  • The root of Valeriana officinalis, used in herbal medicine. 

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