frond vs stipule

frond

noun
  • The leaf of a fern, especially a compound leaf. 

  • Any fern-like leaf or other object resembling a fern leaf. 

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 frond and stipule occurred in a corpus of books? (source: Google Ngram Viewer )