cow parsnip vs hogweed

cow parsnip

noun

  • Any umbelliferous plant of genus Heracleum. 

hogweed

noun

  • Certain plants from the genera Ambrosia, Erigeron, or Heracleum. 

  • An umbelliferous plant, of genus Heracleum, most species of which are phototoxic. 

  • Any coarse weedy herb. 

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