About Armillaria ostoyae (Romagn.) Herink
Like most parasitic fungi, Armillaria ostoyae reproduces sexually. This fungus starts its life cycle as spores, which are released into the environment by a mature mushroom. Spores of this species come in two mating types, which are not categorized as male and female but function similarly to biological sexes. Spores can be dispersed by environmental factors such as wind, or they can be redeposited by animals. After spores enter a resting state, a single spore must come into contact with a spore of the same species that has a complementary mating type. If the two spore isolates come from different species, their colonies will not fuse and will remain separate. When two compatible isolates of the same species with different mating types fuse, they quickly form coalesced, dark brown, flat colonies. This specific fungus produces mycelial cords called rhizomorphs, also commonly known as shoestrings. These rhizomorphs allow the fungus to gather nutrients across long distances, and they are the main factor contributing to the fungus's pathogenicity. As the fruiting body grows and accumulates nutrients, it develops into a mature mushroom. Armillaria ostoyae specifically grows wide, thin gills that radiate decurrently from the stem. The gills produce a white spore print, and the stem retains a well-developed ring. Once spore formation is finished, the mature mushroom can release its spores to begin a new generation. Like several other Armillaria species, the mycelium of A. ostoyae can be bioluminescent, a phenomenon that produces the glowing effect known as foxfire.
Armillaria ostoyae is most common in cooler regions of the northern hemisphere. In North America, it grows on host coniferous trees in the forests of British Columbia and the Pacific Northwest. It also occurs in parts of Asia. While A. ostoyae is distributed across all biogeoclimatic zones of British Columbia, the root disease it causes creates the most severe problems in the interior of the region, specifically in the Interior Cedar Hemlock biogeoclimatic zone. The fungus is present in both the interior of British Columbia, where it is more common, and along the province's coast. A colony of A. ostoyae growing in the Malheur National Forest in the Strawberry Mountains of eastern Oregon has been recorded as the largest fungal colony in the world, spanning an area of 3.5 square miles (9.1 km², 2,200 acres). This organism is estimated to be around 8,000 years old and may weigh up to 35,000 tons. If this colony is counted as a single organism, it is one of the largest known organisms in the world by area; it is only known to be rivaled in size by a colony of Posidonia australis on the Australian seabed that measures 200 square kilometres (77 mi²; 49,000 acres). It also rivals the aspen grove known as "Pando" as the known organism with the highest living biomass. Another well-known large colony called the "humongous fungus" is a specimen of Armillaria gallica found near Crystal Falls, Michigan, which covers 91 acres (0.37 km²; 0.142 sq mi) and originated from a parent fungus in Ontario. Armillaria ostoyae is classified as a choice edible species.
