It sounds like something out of a science fiction novel: a towering, toxic weed that can burn the skin if touched and even cause blindness. 

But giant hogweed is real and is being spotted all across the country, with some worrying the invasive plant is growing out of control.

Giant hogweed, which can grow to 5.5 metres (20 feet), has been popping up just about everywhere this summer, from Vancouver Island -- where it's been a problem for years -- to river banks in Toronto and Ottawa. It's also spreading along roadsides in Nova Scotia and wasteland areas of Newfoundland and Labrador.

Although the plant can be impressive to behold, with its purple, mottled stem, huge leaves, and metre-wide flower head of white blooms, it can pose a threat to anyone who touches it without protective clothing.

Small, blister-like pistules on the plant contain a toxic sap that can burn the skin once exposed to sunlight. If the toxin enters the eye, it can burn the cornea, causing temporary or even permanent blindness.

Experts aren't sure how giant hogweed found its way into Canada or how long it's been here. The plant originates from Asia, and was probably brought into North America decades ago by someone who thought it would make a showstopping ornamental plant.

However it arrived, the weed has become quite invasive in recent years. Earlier this week, Todd Boland, a scientist with Memorial University's Botanical Garden told The Canadian Press that the giant weed is getting out of control in St. John's, saying the city needed to manage it seriously.

The problem with trying to stop giant hogweed is that its large roots make it difficult to dig up. Anyone who tries to do so has to wear full protective clothing, gloves and mask.

Even after it's removed or simply mowed down, the weed can easily reseed itself. Each plant can produce 50,000 winged seeds which can remain viable in the soil for up to 15 years.

Besides the obvious health hazards the plant holds, it also crowds out native species. And because it has relatively shallow roots that don't hold the soil as well as native species, infestations of hogweed can lead to soil erosion along riverbanks.

People who come across the weed are warned to stay clear of it. If you come in contact with the plant:

• find shelter immediately, to stop the sap from photosynthesizing
• wash exposed skin thoroughly with soap and water

The skin can redden 24 hours after exposure. An inflammatory reaction usually occurs after three days. If you have a reaction, you are advised to see a doctor.

Anyone who thinks they've spotted giant hogweed should contact their local municipality to advise them of its location.