Armillaria obscura

This fungus, like most parasitic fungi, reproduces sexually. The fungi begin life as spores, released into the environment by a mature mushroom. There are two mating types for spores (not male and female but similar in effect). Spores can be dispersed by environmental factors such as wind, or they can be redeposited by an animal. Once the spores are in a resting state, the single spore must come in contact with a spore of a complementary mating type and of the same species. If the single spore isolates are from different species, the colonies will not fuse together and they will remain separate. When two isolates of the same species but different mating types fuse together, they soon form coalesced colonies which become dark brown and flat. With this particular fungus it will produce mycelial cords – the shoestrings – also known as rhizomorphs. These rhizomorphs allow the fungus to obtain nutrients over distances. These are also the main factors to its pathogenicity. As the fruiting body continues to grow and obtain nutrients, it forms into a mature mushroom. Armillaria ostoyae in particular grows wide and thin gills, radiating decurrently from the stem. The gills leave a white spore print. Once spore formation is complete, the mature mushroom is able to spread its spores to start a new generation. …

Armillaria ostoyae is mostly common in the cooler regions of the northern hemisphere. In North America, this fungus is found on host coniferous trees in the forests of British Columbia and the Pacific Northwest. It also grows in parts of Asia. While Armillaria ostoyae is distributed throughout the different biogeoclimatic zones of British Columbia, the root disease causes the greatest problem in the interior parts of the region in the Interior Cedar Hemlock biogeoclimatic zone. It is both present in the interior where it is more common as well as along the coast. A mushroom of this type in the Malheur National Forest in the Strawberry Mountains of eastern Oregon, was found to be the largest fungal colony in the world, spanning an area of 3.5 square miles (2,200 acres; 9.1 km2). This organism is estimated to be some 8,000 years old and may weigh as much as 35,000 tons. If this colony is considered a single organism, it is one of the largest known organisms in the world by area, only knowingly rivalled by a colony of Posidonia australis on the Australian seabed that measures 200 square kilometres (77 mi2; 49,000 acres), and rivals the aspen grove "Pando" as the known organism with the highest living biomass. …