Monday 30 May 2011: Magic potion, anyone?
Well, this is your stuff then: Henbane or Stinking Nightshade. Most definitely something cultivated at Hogwarts' School of Witchcraft and Wizardry.
Usage is strictly not recommended though, since it can be toxic, and even fatal in low doses, and it's difficult to know the concentration of the toxic substances in the plant beforehand.
One Year Ago: Forked Spleenwort