Armillaria gallica

Description

Armillaria gallica is a species of honey mushroom in the family Physalacriaceae of the order Agaricales. It is a largely subterranean fungus, and it produces fruit bodies up to 10 cm (3.9 in) in diameter, yellow-brown, and covered with small scales. The gills are white to creamy or pale orange. The stem may be up to 10 cm (3.9 in) long, with a white cobwebby ring that divides the color of the stem into pale orange to brown above, and lighter-colored below.

Usually grows at late-fruiting species, appearing in the colder weather of late fall and early winter or even in the depths of winter, during warm spells. In urban areas it is not uncommon for places where hardwood trees were removed several years beforehand, popping up as a "lawn mushroom" without any immediately obvious relationship to rotting wood through the tree's decaying root system is the actual substrate for the fungus.

Armillaria gallica is considered edible. Thorough cooking is usually recommended, as the raw mushroom tastes acrid when fresh or undercooked. Ultimate Mushroom does not recommend collecting and eating this fungus.

The fungus can develop an extensive system of underground root-like structures, called rhizomorphs, that help it to efficiently decompose dead wood in the temperate broadleaf and mixed forests. The fungus received international attention in the early 1990s when an individual colony living in a Michigan forest was reported to cover an area of 15 hectares (37 acres), weigh at least 95 tonnes (95,000 kg; 210,000 lb), and be 1,500 years old. This individual is popularly known as the "humongous fungus", and is a tourist attraction and inspiration for an annual mushroom-themed festival in Crystal Falls. Recent studies have revised the fungus's age to 2,500 years and its size to about 400 tonnes (400,000 kg; 880,000 lb), four times the original estimate.

Common names: Honey Mushroom, Bulbous Honey Fungus, Václavka Hlízovitá (Czech Republic), Hallimasch (German).

Mushroom Identification

1. Cap

   3–10 cm (1.18–3.9 in); convex, becoming broadly convex or nearly flat; dry or sticky; bald underneath scattered, tiny, yellowish to brownish scales and fibrils (often concentrated over the center); pinkish-brown to tan or, occasionally, yellowish; fading markedly as it dries out; the margin sometimes featuring whitish to yellowish partial veil material when young, becoming lined with age.

2. Gills

   Running down the stem or nearly so; close; short-gills frequent; whitish, discoloring pinkish to brownish.

3. Stem

   4–10 cm (1.57–3.9 in) long; 1–3 cm (0.39–1.18 in) thick; usually club-shaped, with a swollen base; finely lined near the apex; with a yellow ring zone or, occasionally, with a flimsy white ring that features a yellow edge; whitish to brownish when fresh, becoming dark watery brownish to olive-gray from the base upward; base sometimes staining yellow; often attached to black rhizomorphs.

4. Flesh

   Whitish; unchanging when sliced.

5. Odor and Taste

   Odor not distinctive; taste not distinctive, or slightly bitter.

6. Chemical Reactions

   KOH on cap surface yellowish to golden, or negative.

7. Spore Print

   White.

8. Habitat

   "Usually an innocuous saprophyte, living on organic matter in the soil and not harming trees to any great extent" (Volk & Burdsall, 1993); growing on the wood of hardwoods and occasionally on conifer wood; appearing alone, gregariously, or in loose clusters; often appearing terrestrial (but actually attached to roots)—but sometimes fruiting from the bases of trees and stumps; late summer, fall, and winter; widely distributed east of the Rocky Mountains.

9. Microscopic Features

   Spores 7–10 x 4–6 µm; ellipsoid with a fairly prominent apiculus; smooth; hyaline to yellowish in KOH; inamyloid. Basidia 4-sterigmate; basally clamped. Cheilocystidia 15–40 x 2.5–5 µm; cylindric-flexuous to somewhat irregular or contorted; smooth; thin-walled; hyaline in KOH. Pleurocystidia not found. Pileipellis a cutis or ixocutis with areas of upright elements; cutis elements 5–15 µm wide, smooth, hyaline to brownish, with terminal cells cylindric with subclavate to slightly narrowed apices; upright elements 5–15 µm wide, smooth or finely roughened, brownish in KOH, often slightly constricted at septa, with terminal cells cylindric with rounded or slightly narrowed apices.

Look-Alikes

1. Armillaria calvescens

   Similar in appearance, and can only be reliably distinguished from A. gallica by observing microscopic characteristics.

2. Armillaria calvescens

   Has a more northern distribution, and in North America, is rarely found south of the Great Lakes.

3. Armillaria mellea

   Has a thinner stem, but can be more definitively distinguished by the absence of clamps at the base of the basidia.

4. Armillaria ostoyae

   Has more robust, fleshy red-brown fruiting bodies and usually grows on conifer wood.

5. Armillaria cepistipes

   Very similar and characterized by small, darker scales concentrated in the middle of the cap. The scales at the brim of the cap are sparse and disappear quickly. It grows on hardwoods and conifers.

Armillaria gallica Metabolites

This mushroom can produce cyclobutane-containing metabolites such as arnamiol, a natural product that is classified as a sesquiterpenoid aryl ester. Although the specific function of arnamiol is not definitively known, similar chemicals present in other Armillaria species are thought to play a role in inhibiting the growth of antagonistic bacteria or fungi, or in killing cells of the host plant prior to infection.

Armillaria gallica Bioluminescence

The mycelia (but not the fruit bodies) of Armillaria gallica are known to be bioluminescent. Experiments have shown that the intensity of the luminescence is enhanced when the mycelia are disturbed during growth or when they are exposed to fluorescent light. Bioluminescence is caused by the action of luciferases, enzymes that produce light by the oxidation of a luciferin (a pigment).

The biological purpose of bioluminescence in fungi is not definitively known, although several hypotheses have been suggested: it may help attract insects to help with spore dispersal, it may be a by-product of other biochemical functions, or it may help deter heterotrophs that might consume the fungus.

History

The naming and taxonomy of the species now known as Armillaria gallica is confusing and correspond to the species surrounding Armillaria. Until the 1970s, the model species Armillaria was considered a pleomorphic species with a wide distribution, variable pathogenicity, and one of the broadest known host ranges of fungi.

In 1973, Veikko Hintikka reported a technique to differentiate Armillaria species by growing them together as single spore isolates on a petri dish and observing changes in the morphology of the cultures.

The species Korhonen called EBS B was named A.bulbosa by Helga Marxmüller in 1982 because it was equivalent to Armillaria mellea var.bulbosa, first described by Jean Baptiste Barla (Joseph Barla) in 1887, and later bred as this species by Josef Wilenovsky in 1927.

In 1973, the French mycologist Henri Romagnesi, unaware of Velenovský's publication, published a description of the species he called Armillariella bulbosa, based on specimens he had found near Compiègne and Saint-Sauveur-le-Vicomte in France.

In 1987 Romagnesi and Marxmüller renamed EBS E to Armillaria gallica. Another synonym, A. lutea, had originally been described by Claude Casimir Gillet in 1874, and proposed as a name for EBS E. Although the name had priority due to its early publication date, it was rejected as a nomen ambiguum because of a lack of supporting evidence to identify the fungus, including a specimen, type locality, and incomplete collection notes.

The specific epithet gallica is botanical Latin for "French" (from Gallia, "Gaul"), and refers to the type locality. The prior name bulbosa is Latin for "bulb-bearing, bulbous" (from bulbus and the suffix -osa). Armillaria is derived from the Latin armilla, or "bracelet".

Synonyms

1. Armillaria bulbosa (Barla) Kile & Watling

2. Armillaria inflata Velen.

3. Armillaria lutea Gillet

4. Armillaria mellea var. bulbosa Barla

5. Armillariella bulbosa (Barla) Romagn

Photo sources:

Photo 1 - Author: Dan Molter (CC BY-SA 3.0)

Photo 2 - Author: Dan Molter (shroomydan) (CC BY-SA 3.0)

Photo 3 - Author: Christine (CC BY-SA 4.0)

Photo 4 - Author: Amanita77 (CC BY-SA 3.0)

Photo 5 - Author: Henk Monster (CC BY 3.0)