RuneScape Classic Wiki
RuneScape Classic Wiki
The main RuneScape Wiki has an article on: Snake Weed
The Old School RuneScape Wiki also has an article on Snake Weed.

Snake Weed is needed to complete the Jungle Potion and Legend's Quest. It can be found southwest of Tai Bwo Wannai village on Jungle Vines near the coast and inside Strange Barrels.

After the Legend's Quest is done the vines will no longer contain Snake Weed.

Southwest of Tai Bwo Wannai.