Barrelstalk

Barrelstalk was a fungus that grew in the Underdark, named for its barrel-like shape. It had a hard, woody outer surface, but the inside was hollow and could contain about 5 to 8 gallons (19 to 30 liters) of potable water. The inner rings of the barrelstalk were made from an edible pulp. A typical specimen yielded about 5 to 10 pounds (2.3 to 4.5 kilograms) of food.

Some reports of this fungus said that it was only edible when young. Once matured (at about ten years of age), it produced spores and the flesh turned poisonous, making it useless as a source of food and water.