celeriac vs shrub celery

celeriac

noun
  • A form of celery, Apium graveolens, having an aromatic taproot eaten as a vegetable. 

shrub celery

noun
  • The crisp, thick leafstalk of the celery plant; used as a vegetable, or eaten raw. 

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