Madagascar periwinkle vs periwinkle

Madagascar periwinkle

noun
  • The rosy periwinkle, Catharanthus roseus. 

periwinkle

noun
  • Similar plants of genus Catharanthus. 

  • A color with bluish and purplish hues, somewhat light. 

  • Any of several evergreen plants of the genus Vinca with blue or white flowers. 

  • A mollusk of family Littorinidae. 

adj
  • Of pale bluish purple colour. 

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