Giant hogweed could be a pig in a poke for Islanders.

Unwanted, unexpected, unknown, undesirable and a bad bargain — all the synonyms for a pig in a poke could just as easily be applied to this toxic invasive.

Occurrences of this plant have been rising both on and off the Island, but its actual presence is much lower than these reports imply. Blame these concerns (or, like me, thank them) for bringing this danger to the forefront. Consciousness of the plant has been raised on social media where photos circulate, helping folks find and report giant hogweed — and also, at times, misreport its presence due to the fact that it has a few lookalike relatives.

The danger of giant hogweed (Heracleum mantegazzianum) cannot be overstated. This plant, which originated in Central Asia and came to the States in the early 1900s, contains toxic chemicals that cause severe photosensitivity. Within 15 minutes of coming into contact with the plant’s sap — which can be released upon contact with most parts of the plant — skin can burn and blister. And the damage can persist: effects include scarring and long-term light sensitivity. Some reports even suggest that the sap can cause blindness.

If you believe that you have made contact with this problematic plant, get out of the sun immediately! If you can’t, apply sunscreen. Once inside, wash the whole affected area with cold water and even, depending on severity, seek medical attention.

Hogweed is a big — no, giant — plant, reaching up to 18 feet tall and five feet across. It has white clusters of flowers that resemble an open umbrella (such a flower display is known by the similar-sounding term umbel). This dangerous plant generally flowers during the worst possible time for humans — from June through July, when we want to be outdoors.

Interestingly enough, it is a member of the carrot family, but it should never, ever be consumed. Stems of this plant are green with reddish-purple blotches and white hairs. At the stem nodes, you’ll find a ring of coarse white hairs. So, why the confusion? Blame the lookalikes. Two common Island species could claim a resemblance that might confuse the neophyte. The first is cow parsnip, a largish species that flowers around the same time as giant hogweed. In fact, an alias of hogweed is giant cow parsnip because of this likeness. The difference is size and stem. Cow parsnip is smaller and has green stems that lack both the red-purple blotches and the white hairs on the stem nodes.

Another lookalike is blooming now: Queen Anne’s lace, a very popular plant, which has similar flowers, but is much smaller. Don’t be lulled into a false sense of security by giant hogweed’s resemblance to that delicate plant. Considered a noxious invasive species, giant hogweed is, unfortunately, spreading. It is has been found in about 23 communities in Massachusetts, though its presence and persistence change as it is found and eradicated. On the Vineyard to date, it has been located and reported in a few locations in West Tisbury. Luckily, conservation organization staffs work to eradicate these populations as soon as they are found and reported. (Which, by the way, is a good example of how we all benefit from contributing to these organizations.)

This isn’t to say that this malignant plant might not pop up again somewhere else. Anyone who has tried to clear their surroundings of unwanted weeds will understand the reason for skepticism and continuing vigilance. So, do keep your eyes open – and your eyes and your skin protected – if you believe you might have a specimen of this poisonous plant. Reporting its presence is important and most Island conservation groups have staff that can help confirm its identity.

Since the flowering time for giant hogweed has passed, if you see a similar plant the rest of this season, it is likely a lookalike. Don’t be pig-headed about reporting it, as it is always better to be safe than sorry and sunburned.

Suzan Bellincampi is director of the Felix Neck Wildlife Sanctuary in Edgartown, and author of Martha’s Vineyard: A Field Guide to Island Nature.