common reed vs culm

common reed

noun
  • Phragmites australis, a monoculture reed grass. 

culm

noun
  • the stem of a plant, especially of grass or sedge 

  • anthracite, especially when found in small masses 

  • waste coal, used as a poor quality fuel; slack. 

How often have the words common reed and culm occurred in a corpus of books? (source: Google Ngram Viewer )