Bulbous Honey Fungus

The fruit bodies of Armillaria gallica have caps that are 2.5–9.5 cm (1.0–3.7 in) broad, and depending on their age, may range in shape from conical to convex to flattened. The caps are brownish-yellow to brown when moist, often with a darker-colored center; the color tends to fade upon drying. The cap surface is covered with slender fibers (same color as the cap) that are erect, or sloping upwards. When the fruit bodies are young, the underside of the caps have a cottony layer of tissue stretching from the edge of the cap to the stem—a partial veil—which serves to protect the developing gills. As the cap grows in size the membrane is eventually pulled away from the cap to expose the gills. The gills have an adnate (squarely attached) to somewhat decurrent (extending down the length of the stem) attachment to the stem. They are initially white, but age to a creamy or pale orange covered with rust-colored spots. The stem is 4–10 cm (1.6–3.9 in) long and 0.6–1.8 cm (0.24–0.71 in) thick, and almost club-shaped with the base up to 1.3–2.7 cm (0.5–1.1 in) thick. Above the level of the ring, the stem is pale orange to brown, while below it is whitish or pale pink, becoming grayish-brown at the base. The ring is positioned about 0.4–0.9 cm (0.16–0.35 in) below the level of the cap, and may be covered with yellowish to pale-brownish woolly cottony mycelia. …

Armillaria gallica can normally be found on the ground, but sometimes on stumps and logs. Mushrooms that appear to be terrestrial are attached to plant roots underneath the surface. It is widely distributed and has been collected in North America, Europe, and Asia (China, Iran, and Japan). The species has also been found in the Western Cape Province of South Africa, where it is thought to have been introduced from potted plants imported from Europe during the early colonization of Cape Town. In Scandinavia, it is absent in areas with very cold climates, like Finland or Norway, but it is found in southern Sweden. It is thought to be the most prevalent low altitude species of Armillaria in Great Britain and France. The upper limits of its altitude vary by region. In the French Massif Central, it is found up to 1,100 m (3,600 ft), while in Bavaria, which has a more continental climate, the upper limit of distribution reaches 600 m (2,000 ft). In Serbian forests, it is the most common Armillaria between elevations of 70 to 1,450 m (230 to 4,760 ft). Field studies suggest that A. gallica prefers sites that are low in organic matter and have high soil pHs. In North America, it is common east of the Rocky Mountains, but rare in the Pacific Northwest. …

The life cycle of A. gallica includes two diploidization–haploidization events. The first of these is the usual process of cell fusion (forming a diploid) followed by meiosis during the formation of haploid basidiospores. The second event is more cryptic and occurs before fruit body formation. In most basidiomycetous fungi, the hyphae of compatible mating types will fuse to form a two-nucleate, or dikaryotic stage; this stage is not observed in Armillaria species, which have cells that are mostly monokaryotic and diploid. Genetic analyses suggest that the dikaryotic mycelia undergo an extra haploidization event prior to fruit body formation to create a genetic mosaic. These regular and repeating haploidization events result in increased genetic diversity, which helps the fungus to adapt to unfavorable changes in environmental conditions, such as drought. The growth rate of A. gallica rhizomorphs is between 0.3 and 0.6 m (1.0 and 2.0 ft) per year. Population genetic studies of the fungus conducted in the 1990s demonstrated that genetic individuals grow mitotically from a single point of origin to eventually occupy territories that may include many adjacent root systems over large areas (several hectares) of forest floor. Based on the low mutation rates observed in large, long-lived individuals, A. gallica appears to have an especially stable genome. …