Tricholoma ustale

Description

Tricholoma ustale is a species of brown-capped mushroom in the large genus Tricholoma. It is found in Asia, Europe, and North America, though those from North America may represent one or more different species. It is easily overlooked because its cap blends in so well against a background of fallen Beech leaves. It is mycorrhizal with broadleaf trees, notably Beeches and Hornbeams, where it usually occurs in small groups.

Common names: Burnt Knight, Sveden Ridderhat (Danish), Bøkemusserong Brandiger (Norwegian), Ritterling Blassfleischiger (German), Beukenridderzwam (Dutch), Tricholome brûlé (French), Pyökkivalmuska (Finnish), Kakishimeji (Japan).

Mushroom Identification

1. Cap

   A lovely chestnut brown, pale at the margin and darker at the center and often blackening with age, convex, flattening but usually retaining a broad umbo; surface smooth and very viscid in wet weather; 4 to 8cm across when fully expanded.

2. Pileipellis

   Up to 250µm thick, comprising hyphae mainly in the range 2.5 to 6.5µm in diameter, with noticeable banded incrustations.

3. Gills

   Pale creamy grey, developing rusty brown spots with age; crowded; sinuate or emarginate.

4. Stem

   White and fibrous, lined longitudinally with brown fibrils, somewhat darker towards the base; cylindrical or slightly clavate; 3 to 6cm long, 1 to 1.5cm diameter; no ring. The stem flesh is white, turning reddish-brown when cut or bruised.

5. Spores

   Broadly ellipsoidal, smooth, 6-7.5 x 5-6µm, with a noticeable hilum; inamyloid.

6. Spore Print

   White.

7. Odor and Taste

   Odor not significant; taste slightly bitter.

Tricholoma ustale Look-Alikes

1. Tricholoma fulvum

   Occurs in wet grassland under birches.

2. Tricholoma ustuloides

   Is much rarer (in Britain) and has a distinct white region at the stem apex.

3. Tricholoma ezcarayense

   Is similar in appearance to T. ustale, and also grows in association with beech. It can be distinguished in the field by its less robust stature, the minute, flat scales on the cap, and the green tints present in the reddish-brown color of the cap. It can be more reliably distinguished by microscopic characteristics, as the hyphae in its cap cuticle have abundant clamp connections, unlike T. ustale.

Medicinal Properties

History

This mushroom was first described scientifically in 1818 by the great Swedish mycologist Elias Magnus Fries, who named it Agaricus virgatus.

German mycologist Paul Kummer transferred this and several other 'knights' to the genus Tricholoma in 1871.

Synonyms of Tricholoma ustale include Agaricus ustalis Fr., Agaricus fulvellus Fr., and Tricholoma fulvellum (Fr.) Gillet.

Tricholoma was established as a genus by the great Swedish mycologist Elias Magnus Fries. The generic name comes from Greek words meaning 'hairy fringe', and it must be one of the least appropriate mycological genus names, because very few species within this genus have hairy or even shaggily scaly cap margins that would justify the descriptive term.

The specific epithet ustale comes from the Latin adjective ustalis and means burnt - a reference to the color of the cap of this mushroom.

Toxicity

Consumption of the mushroom causes gastrointestinal distress, including symptoms such as vomiting and diarrhoea.

Chemical analysis of Japanese populations has revealed the toxic principles ustalic acid and several related compounds. Force-fed to mice, ustalic acid causes them to sit still in a crouched position, hesitant to move, and induces tremors and abdominal contractions. High enough concentrations of the toxin (10 milligrams per mouse) cause death.

Ustalic acid, an inhibitor of the sodium-potassium pump (Na+/K+-ATPase) found in the plasma membrane of all animal cells, has been chemically synthesized. The toxicity of North American populations is unknown.

Photo sources:

Photo 1 - Author: Holger Krisp (CC BY 3.0)

Photo 2 - Author: Björn S. (CC BY-SA 2.0)

Photo 3 - Author: Lukas from London, England (CC BY-SA 2.0)

Photo 4 - Author: Jerzy Opioła (CC BY-SA 3.0)