Giant hogweed aka giant cow parsley (Heracleum mantegazzianum)
Giant hogweed, a species native to the Caucausus and Central Asia, was introduced in Britain in the 19th century as an ornamental. It has spread subsequently to Continental Europe, Canada, and the United States.
Giant hogweed can grow to a height of 23 feet (7 m.). It is invasive and its sap is highly toxic producing phytophotodermatitis, a chemical reaction causing skin cells to become hypersensitive to ultraviolet light, resulting in blisters, long-lasting scarring, and even blindness.
Giant hogweed has been found to date in Connecticut, Maine, Maryland, Massachusetts, Michigan, New York, New Hampshire, Ohio, Oregon, Pennsylvania, Washington and Vermont.