hedge nettle vs piggyback plant

hedge nettle

piggyback plant

noun
  • A plant native to moist forests near the coast of northwestern North America, Tolmiea menziesii, grown as an ornamental groundcover or container plant for its attractive green foliage with plantlets growing from the bases of the leaves. 

How often have the words hedge nettle and piggyback plant occurred in a corpus of books? (source: Google Ngram Viewer )