hound's tongue vs houndstongue

hound's tongue

noun
  • A biennial weed (Cynoglossum officinale) with soft tongue-shaped leaves and an offensive odour. It bears nutlets covered with barbed or hooked prickles. 

houndstongue

How often have the words hound's tongue and houndstongue occurred in a corpus of books? (source: Google Ngram Viewer )