The Myconid caves are full of level 58-60 aggro Myconids, so you will need to fight if you are level 70 or below (only named mobs are heroic in there now). The watchers can see through invisibility, and presumably sneak, but the others do not see you.
You can enter the cave just north of the Aphotic Intersection, at ( 359, 10, -108 ) /waypoint 359.06, 10.22, -108.12 but you will need to travel some distance (and kill lots of Myconids if 70 or below) before you reach the first fungus node.
To do this quest in the shortest time possible, you can use 2 convenient entrances to the Myconid caves, both of which will put you near the nodes you need for this quest:
Near the waterfall just north of the The Fugutr Tribe at ( 162, -17, -381 ) /waypoint 162, -17, -381.
A pit you can fall down near ( 248, -52, -176 ) /waypoint 248, -52, -176. Caution: Melanog can be at the bottom of the pit.