Giant hogweed
Giant hogweed (Heracleum mantegazzianum) is a very large, 2 to 5 m tall, herbaceous, flowering perennial with many amusing names - Giant Cow Parsley, Hogsbane, and even Giant Alien. However, names are the only thing funny about this plant - it is a phototoxic invasive species. In combination with light, its sap causes phytophotodermatitis, a serious skin inflammation with blistering and scarring which can last for up to several days.