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Honey mushroom

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Honey mushroom
Armillaria mellea.jpg
Scientific Classification
Species
  • A. borealis
  • A. calvescens
  • A. cepistipes
  • A. ectypa
  • A. gallica
  • A. gemina
  • A. heimii
  • A. hinnulea
  • A. laricina
  • A. limonea
  • A. luteobubalina
  • A. mellea
  • A. novae-zelandiae
  • A. obscura
  • A. ostoyae
  • A. sinapina
  • A. socialis
  • A. sparrei
  • A. tabescens
Armillaria ostoyae
Image of Armillaria ostoyae.jpg

Honey mushrooms are a group of mostly saprotrophic (feed on dead organic matter) and parasitic fungi in the genus Armillaria. These mushrooms can be found all over the world. They infect trees by sending out their root-like rhizomorphs which enter and infest the roots of trees. They reproduce both sexually and asexually. Honey mushrooms can be identified by their white spore print and by their gills that are attached to the stem of the fungus[2]. The largest organism in the world is a patch of A. ostoyae growing in Oregon. It is thought to be over 2,200 years old and it covers over 2,400 acres of land[3].

Anatomy

A close up view of A. ostoyae's gills and stem.

All fungi placed in the genus Armillaria are white-spored, wood-rotting, and have gills that are attached to the stem of the fungus[4]. The honey mushroom’s cap can range between three to twenty centimeters in length. The cap itself can be either flat or have a convex shape. The older the mushroom is, the more likely it will have a flatter cap. Depending on the environment the cap may be slightly moist or dry. The cap’s color may be various shades of brown[5].

The gills of the honey mushroom are one of its distinguishing characteristics because they are always attached to the stem of the fungus[5]. Gills are plate like structures that are organized underneath the mushroom’s cap. They are very important and used to help identify many species[2]. In honey mushrooms, the gills tend to partially run down the stem as well as be located under the cap. Mostly these gills will have a pinkish color however there may be red or brown spots that can discolor the gills[5].

The honey mushroom’s stem is white and fleshy. It is six to fifteen centimeters long and two to three centimeters thick. Mycelia (a mat or complex web of hair shaped fibers) are found at the base of the honey mushroom's stem. These rhizomorphs (strands of mycelium) can stretch out for miles underground[2].

Reproduction

Honey mushrooms can reproduce both sexually and asexually. The most common form is asexual reproduction. Honey mushrooms have a form of asexual reproduction involving their hyphae (another name for their black root-like structures). The hyphae grow by producing more cells at the tip of the strand. These root-like structures are very strong and allow the mushroom to break through the wood of trees. If a section of hyphae breaks off, it will continue to grow as a clone, a genetically identical organism. These separate structures can then form stalks and caps. After they form caps they can begin to sexually reproduce[6].

Honey mushrooms also reproduce sexually. They do this by the production of spores. A spore is a cell wall that protects cytoplasm and a nucleus. The spores are produced under the cap in the gills[7]. When the spore caps mature, they break open releasing their spores. These spores are then carried by the rain or wind to new locations. Once they land they will germinate (grow or sprout) like a seed. However if they do not land in an area with favorable conditions, the spores can go into a dormant state as they wait for conditions to improve[6].

Ecology

Honey mushrooms can be found all over the world. They fruit (produce a cap) for almost the entire year in warmer climates. In North America, armillaria generally fruit in late summer and throughout the fall. As its name implies, its cap has a sweet flavor. The most well known species is A. mellea[3].

Some species of honey mushrooms are saprotrophs, which means that they feed on dead material. Others are parasitic, and prey on the roots and the trunks of living trees. The honey mushrooms are most often to blame for white rot found in wood. The mushrooms infect trees and roots by sending out their rhizomorphs. These rhizomorphs are long black, stringy tendrils that are composed of fungus cells. Once sent out, they are used to channel nutrients and help to extend the contamination of the fungus. One species of honey mushroom, Armillaria solidipes, is one of if not the largest organism in the world. One specimen is thought to be over 2,200 years old. Over the years it has spread mostly through sending out its rhizomorphs. This single patch of underground mycelia (rhizomorphs) covers over 2,400 acres in Oregon[3].

Armillaria Root Rot

A. gallica at the base of a tree.

Armillaria is the most common root rot in the Pacific Northwest. It is caused by the spread of parasitic fungi known as honey mushrooms. Trees are infected by the mushroom’s rhizomorphs. These rhizomorphs grow through the soil and penetrate directly into the roots of trees. Younger trees quickly die when they become infected while older trees can survive for many years after an infection. These older trees will be in a weaken state as they try to block the infection. All coniferous species are susceptible to becoming infected[8].

Here are several ways to identify a tree that is infected. The most obvious way to tell is the presence of honey-colored mushrooms near the base of the tree during fall months. A lack of cones produced by the tree is also an indicator. If you check the roots you should be able to see the black rhizomorphs penetrating the roots. Armillaria root rot may also occur alongside other types of root disease[8].

Video

Harmful honey mushrooms found on the stump and roots of a tree.

Gallery

References

  1. Armillaria EOL. Web. 5-19-2013(Date-of-access).
  2. 2.0 2.1 2.2 Kuo,M. Glossary of Mycological Terms MushroomExpert.Com. Web. February, 2006 (Date-of-publication).
  3. 3.0 3.1 3.2 Honey-fungus Mushroom-Appreciation.com. Web. 5-19-13(Date-of-Access).
  4. Kuo,M. The-Genus-Armillaria MushroomExpert.Com. Web. February,2005 (Date-of Publication).
  5. 5.0 5.1 5.2 Kuo,M. Armillaria-ostoyae MushroomExpert.Com. Web. February, 2008 (Date-of-publication).
  6. 6.0 6.1 Fungi Microbeworld.org. Web. May 27, 2013(Date-of-access).
  7. Mushroom-Spores SalviaSupply.com. Web. March 27, 2013(Date-of-access).
  8. 8.0 8.1 ARMILLARIA-ROOT-ROT WSU-DNR-Forest-Health. Web. May 27,2013(Date-of-access).