Armillaria solidipes 28-4 v1.0
Figure 1.  Fruit bodies of A. solidipes.  The largest fruit body is approximately 12 cm in length. (photo by Myron L. Smith)
Figure 1. Fruit bodies of A. solidipes. The largest fruit body is approximately 12 cm in length. (photo by Myron L. Smith)

Armillaria solidipes (Romangnesi) Herink (formerly called A. ostoyae) is one of many species of the genus collectively known as shoestring root-rot fungi or honey mushrooms. A. solidipes is a nearly ubiquitous invader and pathogen of softwood trees in northern temperate forests. The effect of the fungus on its host ranges from lethal to nearly negligible. Newly planted pines in recently cleared mixed hardwood forests are particularly susceptible to damage by the fungus. Mating in populations of A. solidipes is effectively random over continental scales, presumably due to the dispersal of air-born basidiospores. Specificity in mating is controlled by the bifactorial sexual incompatibility system typical of many basidiomycetes, but the predominant vegetative phase of A. solidipes is diploid, not dikaryotic as in most other basidiomycetes. In nature, each individual of A. solidipes originates in a unique mating event and the resultant diploid mycelium may colonize a territory encompassing many adjacent tree root systems. Many individuals are large, extending over many hectares of forest floor, and old, often in excess of 1000 years. One such individual in the Malheur national Forest, Washington, USA extends over nearly 1000 hectares; the genome sequence for this species therefore represents some of the largest individuals on earth. Because of its large geographic distribution, large biomass per unit area of forest, and formidable capabilities as a pathogen and wood degrader, A. solidipes is likely to play an important role in global carbon cycling.