Professor Pomona Sprout is an old hand at teaching, having been at it for longer than most people have been alive, and after a good sixty-odd years at Hogwarts decided to go for something a little more challenging. St Trinian's seemed about the sort of thing she was after.
She looks harmless, with her flyaway, grey hair and grandmotherly features, and despite her rather blazé methods of teaching a class, she's found that bribery and corruption work better than threats at keeping her classes under control. Herbology used to be her subject, indeed several of her pet plants can be found wandering her classroom, but now she's in charge of Environmental Science at this new school of hers. Most of the time she manages to remember that it's Muggle knowledge she's supposed to be teaching but at least it makes the practicals interesting.
Bug her for a pot of tea, if you dare like, she makes up the ingredients herself and, considering her academic speciality, she can come up with some rather special blends.
Professor Pomona Sprout is an entirely fictional creation created for the RPG old_school_ties which you should all join. She belongs entirely to J.K.Rowling who wrote the Harry Potter books in which Pomona features and actually has nothing to do with Helen Mirren whose photo credit she uses. She'd also like to point out that this is all for entertainment purposes, her own specifically, and no profit is being made.