page_title: Armillaria ostoyae
section_title: Taxonomy
hierarchical_section_title: Armillaria ostoyae / Taxonomy
caption_attribution_description: English: The mushrooms Armillaria ostoyae (Romagn.) Herink. Photographed in Santa Cruz, Santa Cruz Co., California, USA. "Notes: Found these right behind the UCSC water tanks."
context_page_description: Armillaria ostoyae is a species of plant-pathogenic fungus in the family Physalacriaceae. It is the most common variant, in the western United States, of the group of species under the name Armillaria mellea. Armillaria ostoyae is common on both hardwood and conifer wood in forests west of the Cascade Range in Oregon, United States. It has decurrent gills and the stipe has a ring. The mycelium invades the sapwood and is able to disseminate over great distances under the bark or between trees in the form of black rhizomorphs. In most areas of North America, Armillaria ostoyae can be separated from other species by its physical features: cream-brown colors, prominent cap scales, and well-developed stem ring distinguish it from any Armillaria.
  It is known as having grown possibly the largest living organism by area – estimated by scientists as a contiguous specimen found in the Oregon Malheur National Forest covering 3.7 square miles – and colloquially called the "Humongous fungus". Armillaria ostoyae grows and spreads primarily underground and the bulk of the organism lies in the ground, out of sight, making it invisible from the surface.
context_section_description: The species was long known as Armillaria ostoyae Romagn., until a 2008 publication revealed that the species had been described under the earlier name Armillaria solidipes by Charles Horton Peck in 1900, long before Henri Romagnesi had described it in 1970. Subsequently, a proposal to conserve the name Armillaria ostoyae was published in 2011 and has been approved by the Nomenclature Committee for Fungi. This fungus harms conifer trees in the U.S and Canada.
caption: Armillaria ostoyae
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