Indian potato vs hopniss

Indian potato

noun
  • Sagittaria latifolia (broadleaf arrowhead, duck potato), an aquatic plant native to North and South America. 

  • Orogenia spp. (now in Lomatium), a terrestrial plant native to western North America; 

  • Apios americana (American potato-bean), a terrestrial plant native to eastern North America; 

hopniss

noun
  • Apios americana, a perennial vine that bears edible beans and large edible tubers. 

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