Honey mushroom (Armillaria ostoyae)

Honey mushroom, fruiting bodies

Top facts

  • The honey mushroom is the largest living organism in the world, with its underground growth stretching up to ten square kilometres.
  • Despite its vast size, only a small percentage of the honey mushroom’s growth is visible above ground.
  • The enormous honey mushroom fungus can weigh around as much as a blue whale.
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Honey mushroom fact file

Honey mushroom description

GenusArmillaria (1)

The honey mushroom (Armillaria ostoyae) is the largest living organism in the world, although only a small percentage of its growth is visible above ground (4). The fungus’s cap can vary between tan, yellow-brown and dark red, and is covered in darker fibrous scales, especially around the centre (2) (3) (5) (6). The stem is yellow and rounded at the base, gradually becoming red-brown towards the cap (3) (5). There is a white, cotton-like veil towards the top of the stem (2). The gills on the underside of the cap are white in young growth, becoming yellow then pink-brown as the fungus ages (3) (5).

The fruiting bodies of the honey mushroom can be found growing in large clusters, as well as alone (2) (3).

Also known as
dark honey fungus, honey-coloured mushroom.
Agaricus obscurus, Armillaria obscura, Armillaria polymyces, Armillaria solidipes, Armillariella ostoyae, Armillariella polymyces.
Cap width: 2.5 - 9 cm (2)
Stalk length: 5 - 20 cm (3)
Stalk thickness: 1 - 2.5 cm (2)
Underground growth area: up to 10 square km (4)

Honey mushroom biology

The honey mushroom is saprophytic and absorbs nutrients from soil and dead plant matter such as leaf litter or rotten wood (8). To do this, the honey mushroom uses an underground system of thick, brown, root-like hyphae, which permeate the food source and take up the nutrients (2) (6). This particular fungus is an effective decomposer of wood (2).

The fruiting body of the honey mushroom is mostly present above ground between July and November (3).


Honey mushroom range

The honey mushroom is found worldwide in northern parts of North America, Europe and Asia (7).


Honey mushroom habitat

The honey mushroom is usually found living on the trunks and stumps of broad-leaved, deciduous and coniferous trees (5) (6), including aspen (Populus spp.) and balsam poplar (Populus balsamifera), and less frequently birch (Betula spp.) (2).


Honey mushroom status

The honey mushroom has yet to be classified by the IUCN.


Honey mushroom threats

There are not known to be any threats currently facing the honey mushroom.


Honey mushroom conservation

There are not known to be any specific conservation measures currently in place for the honey mushroom.


Find out more

Find out more about the honey mushroom:

Find out more about fungi:



This information is awaiting authentication by a species expert, and will be updated as soon as possible. If you are able to help please contact:



A plant that sheds its leaves at the end of the growing season.
The branching, threadlike filaments that make up the vegetative (non-reproductive) part of a fungus.
Term applied to a plant or plant-like organism that absorbs nutrients from dead plant or animal matter.


  1. Species 2000 and ITIS Catalogue of Life(July, 2012)
  2. Laursen, G.A. and Seppelt, R.D. (2009) Common Interior Alaska Crytogams:Fungi, Lichenicolous Fungi, Lichenized Fungi, Slime Molds, Mosses and Liverworts. University of Alaska Press, Alaska.
  3. Bessette, A.B., Bessette, A.R and Fischer, D.W. (1997)Mushrooms of Northeastern North America. Syracuse University Press, New York.
  4. Wearing, J. (2010) Fungi:Mushrooms, Toadstools, Molds, Yeasts and Other Fungi. Crabtree Publishing Company, Ontario.
  5. Phillips, R. (2006) Mushrooms. Macmillan, London.
  6. Courtecuisse, R. (1999) Mushrooms of Britain and Europe. HarperCollins, London.
  7. Hanna, J.W., Klopfenstein, N.B., Kim M.S., McDonald, G.I. and Moore, J.A. (2007) Phylogeography of Armillaria ostoyae in the western United States. University of Idaho, Moscow, Idaho. Available at:
  8. Lavender, D.P. (1990) Regenerating British Colombia’s Forests. University of British Colombia Press, Vancouver.

Image credit

Honey mushroom, fruiting bodies  
Honey mushroom, fruiting bodies

© Philippe Clement / naturepl.com

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