fern-leaf vs stipule

fern-leaf

noun
  • The leaf of a fern; used attributively in various terms (see Derived terms below). 

stipule

noun
  • A basal appendage of a typical leaf of a flowering plant, usually appearing paired beside the petiole although sometimes absent or highly modified. 

How often have the words fern-leaf and stipule occurred in a corpus of books? (source: Google Ngram Viewer )