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My son picked a leaf off this plant and rubbed it on his face to see how soft it was (bad idea, I know). Within 12 hours he had a lesion with weeping blisters which we suspect is photosensitive. A prescription med and keeping it covered is helping, but we’d like to know what it is. The leaf is huge - 13cm wide and 38 cm long. It was growing in an old hay field in eastern Ontario. It does not seem to be Wild Hogweed or Parsnip. Can anyone help identify it?enter image description here

  • Difficult to say. TO me seems some Brassicaceae. I do not remember photo-sensible plants in this family. Anyway some people and kids are hyper-sensible to various plants. Wait for the flowers. But many plants could do problems: kids (and adults) should not eat berry randomly nor rubs vegetables. Jun 22, 2018 at 8:31

3 Answers 3


This looks like horseradish or Armoracia rusticana to me. I have some in my backyard I cannot get rid of. The leaves look like it and are described as variable in size and serration.
Horseradish leaves by Justin Brower

This site has pictures which are similar. The description sounds quite painful

When the leaves or roots of a horseradish plant are chewed by a predator, the cells are burst open and release sinigrin, a glucosinolate. When exposed to sinigrin . . . . nothing happens. But wait, also released from the cells is the enzyme myrosinase. This enzyme acts as a catalyst, or blasting cap, and hydrolyses (adds water to) sinigrin into glucose and allyl isothiocyanate. Isothiocyantes are some of the worst chemicals you can work with. They irritate your eyes, burn your lungs, smell horrible, and goes downhill from there. Every synthetic chemist has an isothiocyante story that they wish they could forget

  • OUCH! The leaf nervature looks strikingly similar with the parallels in the center that then fan out into a much finer structure. Good find!
    – Stephie
    Jun 24, 2018 at 17:57
  • OTOH we eat the roots without problems (and I think Wasabi is very similar). Similar to many vegetables, they could be nutriments for some animals and high poisons for other animals. BTW I'm trying to expand it: a lot of manure seems the right way. Jun 25, 2018 at 9:27
  • @GiacomoCatenazzi To get it to grow more just try and dig it out! That's what happened to mine.
    – kevinskio
    Jun 25, 2018 at 11:08

Could it be a tobacco plant? That was my first thought, but I dont know about in your region

  • Any photos I can find of tobacco leaf do not show serrated edges as in the OP's photo.
    – renesis
    Jun 21, 2018 at 23:34

This plant is likely Elecampane (Inula helenium). It is dramatically present with its big leaves and bright big daisy type flowers on Ontario roadsides in summer and seems to be increasingly so. It is not really known as a phytotoxic plant but anything is possible - bear in mind that this might not be the only plant that people can come in contact with. I frequently see people collecting specimens for domestic display and it is not known here as poisonous even though all plants to some degree contain odd chemicals by their very nature.

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