Blog & News

Giant Hogweed – A Fearsome Invasive Plant! (archive)

Published on Wednesday October 15, 2014

Authored by PEIISC

I think this post is fitting since Halloween is just around the corner!

One of the most fearsome invasive plants out there has got to be Giant Hogweed (Heracleum Mantegazzianum). It is indeed a giant, often standing 5 metres tall with an umbrella-shaped flowering portion that can be 1.5 metres across. Perhaps the scariest part of Giant Hogweed is the effect its sap can have on human skin.

Giant Hogweed sap can cause severe photodermatitis in humans – that is, if Giant Hogweed sap touches your skin, it will cause burning and blistering if the affected area is exposed to sunlight. This painful effect can last for years, and if the sap reaches your eyes it can cause permanent blindness. Perhaps it is these terrifying traits that make people extra vigilant in reporting (what they believe is) Giant Hogweed. Every year we receive a couple reports of Giant Hogweed on PEI. Every time, so far, it has been a case of mistaken identity.

Giant Hogweed has a couple of look-alikes on PEI. Cow Parsnip (Heracleum maximum) and Queen Anne’s Lace/Wild Carrot (Daucus carota) are two species commonly mistaken for Giant Hogweed. The following photos and notes should help in identifying Giant Hogweed and distinguishing between it and its look-alikes.

– Julie-Lynn Zahavich, PEIISC Member

Attached images:

The flowering portion of Giant Hogweed (middle) is umbrella-shaped (rounded top) and can grow to be 1.5 metres wide. The flowering portion of Cow Parsnip (left) is flat-topped and does not usually exceed 1 foot across. Queen Anne’s Lace (right) flowers grow in flat-topped umbels that are usually only 6-15 cm across.

Queen Anne’s Lace growing along the Confederation Trail

Giant Hogweed (top) and Cow Parsnip (bottom) leaves are very similar. Both are compound with jagged edges and 3 leaflets. However, Giant Hogweed leaves can reach 5 feet wide, while Cow Parsnip leaves grow to be only 2 -2.5 feet wide. Queen Anne’s Lace (not pictured) leaves are feathery and resemble carrot leaves, like the ones you might grow in your garden.