Tricholoma acerbum

What You Should Know

Tricholoma acerbum is a mushroom of the agaric family Tricholomataceae. Its large size and its pale ochre cap with and strongly inrolled margin are usually enough to convince anyone who has previously seen a few of these massive mushrooms. It is found in Europe and North America.

This mushroom is known to be slightly toxic and should not be collected for the pot. Even when thoroughly cooked these chunky mushrooms can cause gastric upsets if they are eaten.

Other names: Bitter Knight, Sīvā pūkaine (Latvia), räffelmusseron (Sweden), Gorka vitezovka (Serbia), čírovka horká (Slovakia), Rihvelheinik (Estonia), čirůvka hořká (Czech Republic), Krulzoomridderzwam (Netherlands).

Tricholoma acerbum Mushroom Identification

1. Cap

   8-12 (15) cm, initially hemispheric-globose, then convex and finally outstretched; edge initially strongly inrolled, almost touching the stem, then inrolled and ribbed. The cuticle is thick, almost detachable, smooth, tomentose and felted particularly at the edge, matt in dry weather, glossy and bright and rather greasy in wet weather. The color is yellow-ochre, beige-yellowish, yellow-greenish, and cream-brownish at the center in the ripe specimens.

2. Hymenium

   Thick gills, little trimmed on the margin, weakly decurrent with thread, sinuate, narrow, intercalated by several lamellulas which, at times, merge tightly with the gills, thus forming furcations, white, white-cream, cream-pale yellow, they tend to cover with brown dots when ripe.

3. Stipe

   6-10 x 2-4 cm, cylindraceous, sturdy, full, thinner bellow, concolorous to the cap in the lower part, powdery, pale in the first upper third, decorated with brown granumations increasing with the ripening.

4. Flesh

   Thick, firm, compact, immutable white, brownish after long exposure time to the air or when exsiccated. Almost nil smell, astringent taste, bitterish.

5. Habitat

   It grows in summer and autumn under broad-leaved trees, especially chestnuts and oaks, abundant in the locations of growth.

6. Spore Print

   White.

7. Microscopy

   Ellipsoidal spores, smooth, uniguttulate, 4,5-5,5 × 3,5-4,5 µm. Q = 1,26. Basidia are clavate, cylindrical without joints to buckle, 25-33 × 5,5-6,5 µm.

8. Similar Species

   Tricholoma roseocerbum has on the cap some pink, pink-brown, hues and, after the literature, grows in woods of broad-leaved trees as well as in those of conifers, apart the color of the cap, macroscopically there are no differences and also the microscopy is almost overlapping.

Tricholoma acerbum Taxonomy and Etymology

When Jean Baptiste Francois (Pierre) Bulliard described this woodland mushroom in 1792 he gave it the binomial scientific name Agaricus acerbus.

Eighty years later, in 1872, French mycologist Lucien Quélet renamed this species Tricholoma acerbum, which is the name by which mycologists generally refer to it nowadays.

The only synonyms of Tricholoma acerbum that I am aware of are Agaricus acerbus Bull., and Gyrophilus acerba Quél.

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 acerbum means bitter, a reference to the taste of these chunky woodland mushrooms.

Sources:

Photo 1 - Author: alelicciardello (Attribution-NonCommercial 4.0 International)

Photo 2 - Author: filipfuljer (Attribution-NonCommercial 4.0 International)