Jimson weed is of the genus Datura of which there are many species. There are many hybrids out these days with single and double purple,yellow and white flowers. A relative of datura and often confused with it is Brugmansia. These can grow to almost treelike proportions in warm climates and have long drooping trumpet shaped blooms in white, pink, yellow, orange and all shades in between. Daturas and Brugmansias are not releated (not even closely) to helleborus.
Hate to burst a bubble but I think Jimson weed got its name from the old Jamestown settlement...the inhabitants were starving to death and ate this...on arriving on the scene someone somewhere in a history book said they were a crazed bunch..."sitting in trees and yewling like monkeys..." or something like that. Somebody help me out here.