From Guild Wars 2 Wiki
Deadly Nightshade is a trophy required for the HOPE I: Research legendary weapon collection.“
— In-game description
AcquisitionClimb to the vista inside Lightfoot Passage to the southeast of Thunderhead Waypoint — in the Straits of Devastation, then interact with the Deadly Nightshade. Choose the option to "Carefully cut the flower near the ground."
| Vial of Potent Hylek Poison
(Learned from: Recipe: Vial of Potent Hylek Poison)