Stormvine can be gathered by a a herbalist at level 490 and was introduced for the Cataclysm Expansion. Stormvine can only be found in Cataclysm maps like Mount Hyjal, Abyssal Depths, Shimmering Expanse and Kelp’thar Forest. The best zone to farm for Stormvine would be Mount Hyjal. Stormvine is usually found Mount Hyjal on the grass and at the foot of the mountains.
See below for maps to farm Stormvine,