Yes. They were indeed going to learn about disgusting aquatic plants. How fortunate. The word gillyweed did ring a bell for Ariadne, but it was more related to history than Herbology. Not surprisingly, since history was the girl's favourite subject. 'Harry Potter used gillyweed to breathe underwater during the second task of the Triwizard Tournament in 1995.' the Gryffindor firstie replied, after having raised her hand.