I recently encountered a plant that took a bit of research to identify: Henbane or Hyoscyamus niger (LINN.)
It's considered to be an invasive species found throughout Central and Southern Europe and in Western Asia, extending to India and Siberia. As a weed of cultivation it now grows also in North America and Brazil. It had become naturalized in North America prior to 1672, as we find it mentioned in a work published in that year among the plants 'sprung up since the English planted and kept cattle in New England.'
The medicinal uses of Henbane date from remote ages; it was well known to the Ancients, being particularly commended by Dioscorides (first century A.D.), who used it to procure sleep and allay pains, and Celsus (same period) and others made use of it for the same purpose, internally and externally, though Pliny declared it to be 'of the nature of wine and therefore offensive to the understanding.'
All parts of the plant contain scopolamine, atropine, and hyoscyamine and can be deadly poisonous.
It is supposed that this is the noxious herb referred to by Shakespeare in Hamlet:
'Sleeping within mine orchard,
My custom always of the afternoon
Upon my secure hour thy uncle stole,
With juice of cursed hebenon in a vial,
And in the porches of mine ear did pour
The leprous distillment.'
For a plant considered to invasive and noxious, it's quite attractive. The flowers are yellowish-green, bell shaped and covered with a delicate webbing in purple - attractive on the surface, but hiding a possibly dangerous secret nature.