Jamestown weed is often more commonly known as "jimsonweed" or simply "jimpson". It is a poisonous annual plant (Datura stramonium) in the nightshade family (Solanaceae). It has stinky leaves and white trumpet-shaped blooms and is the source of many useful alkaloids, including atropine, hyoscine and hyoscyamine.

Reputedly, the early settlers in Jamestown, Virginia discovered the toxic effects of the plant when a cook mistakenly collected several of them to make a side dish of greens to a meal.

From the science dictionary at http://biotech.icmb.utexas.edu/.