From Guild Wars 2 Wiki
Mysterious Seed is one of many items needed to craft a Mysterious Vine backpiece.“
— In-game description
|Azarr Softhoof||Uplands Oasis||1|
- You will need to complete various chapters of the Living World Season 2 if you are aiming for all the backpieces available. Only the Mysterious Vine can be acquired without having to purchase anything.