kidney vetch vs lamb's ears

kidney vetch

noun
  • Anthyllis vulneraria, a medical plant in the pea family 

lamb's ears

noun
  • Stachys byzantina, an ornamental low-growing perennial related to betony with soft, silky hairs on the leaves which give it an attractive silvery-gray color. 

  • Used other than figuratively or idiomatically: see lamb, ear. 

How often have the words kidney vetch and lamb's ears occurred in a corpus of books? (source: Google Ngram Viewer )