Ghost Mushroom

Ghost Mushroom is a Herb that can be gathered by Herbalists. It requires 245 in Herbalism to gather.

Source
As far as Azeroth goes, Ghost Mushrooms can be found only in The Hinterlands (in the cave beneath Skulk Rock, and in the cave near the altar in Jintha'Alor), Razorfen Downs, Maraudon and Dire Maul. They grow exclusively underground. Each node yields only one Ghost Mushroom with a relatively high respawn time compared to other herbs.

In Outland, they have been spotted in caves in Zangarmarsh. The frequency of spawns seems to be dramatically higher in these caves than in Azeroth. A popular spot is the Funggor Cavern, in the south-eastern part of Zangarmarsh. Often up to three nodes are spotted at one time.

Nature elementals such as Irontree Stompers, Irontree Wanderers, Withered Protectors, and all the Warpwood mobs in Felwood will occasionally drop a Ghost Mushroom.

With the update of the Darkmoon Faire, a player is able to purchase up to 4 Ghost Mushrooms (limited supply) for 15 silver each from Lhara.

Pickable Zones

 * The Hinterlands	61.0%
 * Maraudon	37.8%
 * Zangarmarsh	1.2%

Ghost Mushroom as an Ingredient
Ghost Mushroom is used in the following recipes:

Alchemy

 * Elixir of Demonslaying
 * Elixir of Shadow Power
 * Ghost Dye
 * Invisibility Potion
 * Limited Invulnerability Potion

Inscription

 * Violet Pigment
 * Ruby Pigment