perianth vs perigonium

perianth

noun

  • The sterile parts of a flower; collectively, the sepals and petals (or tepals). 

  • The sterile, tubelike tissue that surrounds the female reproductive structure in a leafy liverwort. 

perigonium

noun

  • The sterile parts of a flower; collectively, the sepals and petals (or tepals); the perianth. 

  • The modified leaves around the antheridia in a bryophytic plant. 

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