Porphyrellus porphyrosporus

Description

Porphyrellus porphyrosporus is a type of mushroom that belongs to the Boletaceae family. It is difficult to spot due to its purple-brown cap and stem and can be found growing under pine and deciduous trees. Its most distinctive features are the purple-brown spore print and the blue-green color of the flesh at the top of the stem and above the hymenium.

It is commonly found in Europe and North America throughout the Pacific Northwest, including Michigan, California, Nova Scotia, and Washington, and appears from late summer to autumn, often in small groups, associated with broad-leaved trees such as beech and oak. It has a dry, velvety cap that is dark brown to olive-brown or dark vinaceous brown, white flesh that turns blue then reddish brown when exposed, brown pores when young, tubes that become blue when bruised or exposed, and a cap-colored stem that may be reticulate.

There is ongoing debate over its classification and synonyms and DNA testing has moved it into the newly erected genus “Porphyrellus.”

It was once considered edible, but recent findings have revealed a slight toxicity.

Common names: Dark Bolete, Dusky Bolete, Düsterer Röhrling (German), Hřib Nachovýtrusý (Czech Republic).

Mushroom Identification

1. Cap

   6-15 cm wide when mature, starts out as convex and becomes irregular and uneven with age. The surface is dull, unpolished, and hairy, with a color of sooty black to very dark brown, sometimes darker in the middle and lighter on the edges. The edges are straight and can be curved or bent. Context is 1-2 cm thick, white, and may turn blue or pink when cut. It also stains wax paper dark blue-green.

2. Tubes

   1.5-2 cm long and shorter towards the edges. It's deeply and broadly to narrowly depressed, and dark brown to almost black in color. The color is slightly lighter on the edges and turns blue when bruised, then changes to purplish-brown. The pores are up to 1 mm wide, irregularly distributed and concolorous with the tubes. They also turn blue when bruised and then change to dark mahogany brown.

3. Stem

   The stem is 13-20 cm long and 1.5-2 cm thick at the top, it's clavate to subclavate, solid to stuffed. It's dry, dull, and glabrous, with longitudinally ridged and often somewhat reticulate, dark brown in color and staining reddish vinaceous when first bruised and then dark brown to black. Sometimes there are areas that stain blue and it's whitish at the base. Context is pale pinkish-tan, becoming pale flesh color when exposed.

4. Spores

   13.8-17.6 X 6-9.6 ľm, dark ochraceous in Melzer's, pale yellow in KOH, smooth, thick-walled, subfusoid to subcylindric to subovoid in face view, inequilateral in side view, no apical pore.

5. Spore Print

   Deep reddish-brown / purple-brown.

6. Basidia

   30-45 X 10-15 ľm, clavate, four-spored, hyaline; irregular areas in hymenium staining dark brown in KOH. Hymenial cystidia 36-51 X I2-15 ľm, abundant, cinnamon brown in KOH, chocolate brown in Melzer's, embedded in the hymenium, fusoid-ventricose to mucronate to clavate with elongated, tapering apices.

7. Tube

   Trama divergent, hyaline, appearing somewhat gelatinous in KOH, hyphae ą8 um wide. Pileus trama interwoven, hyaline except for scattered areas that stain brown in KOH, homogeneous. Pileus cuticle differentiated as a trichodermium, which frequently collapses with age, with scattered free hyphal tips colored cinnamon-brown in KOH, not incrusted, contents of cells staining brown in KOH, hyphae up to 10 ľm wide. Stipe cuticle is differentiated as a tangled trichodermium that stains cinnamon-brown in KOH. Clamp connections absent.

8. Odor and Taste

   Odor is often strong and pungent. Taste is not distinctive. Older fruiting bodies have an unpleasant kerosene-like smell.

9. Chemical reactions

   KOH-cuticle dark red, context red; HN03, HCL, and H2SO4-context pink, cuticle bright red; sulfoformalin-context and cuticle red; FeS04-cuticle dark gray.

10. Habitat

    The mushroom grows from July to October in coniferous and mixed forests, on sandy soils.

Look-Alikes

1. Imleria badia

   Similar, but with a shiny cap when fully developed. Its tubes turn blue when bruised.

History

The Dusky Bolete, first described in 1835 by Elias Magnus Fries and Fredrik Christopher Theodor Hök as Boletus porphyrosporus in their thesis Boleti, Fungorum generis, illustratio, was later transferred to the genus Porphyrellus by French mycologist Jean-Edouard Gilbert in 1945. The mushroom gets its name from its dark purplish-brown colors.

Synonyms and Varieties

• Boletus asprellus Fries (1838) [1836-38], Epicrisis systematis mycologici, p. 423

• Boletus asprellus var. longipes Fries (1874), Hymenomycetes europaei sive epicriseos systematis mycologici, p. 514

• Boletus cinereus ss. Krombholz (1836), Naturgetreue abbildungen und beschreibungen der essbaren, schädlichen und verdächtigen schwämme, 5, p. 2, tab. 4, fig. 26-27

• Boletus olivaceobrunneus Zeller and Bailey, Mycologia 27:457. 1935

• Boletus porphyrosporus Fr. & Hök, Boleti, 1835

• Boletus porphyrosporus var. minor Bataille & Crawshay (1924) [1923], Bulletin trimestriel de la Société mycologique de France, 39(4), p. 267

• Boletus porphyrosporus var. porphyrosporus Fr. (1835)

• Boletus pseudoscaber Secretan (1833), Mycographie Suisse, 3, p. 13

• Boletus sterbeeckii J. Kickx f. (1849), in Fries, Summa vegetabilium Scandinaviae, 2, p. 317

• Gyroporus asprellus (Fries) Quélet (1886), Enchiridion fungorum in Europa media et praesertim in Gallia vigentium, p. 162

• Gyroporus porphyrosporus (Fries) Quélet (1886), Enchiridion fungorum in Europa media et praesertim in Gallia vigentium, p. 162

• Krombholzia asprella (Fries) P. Karsten (1882), Bidrag till kännedom af Finlands natur och folk, 37, p. 18

• Krombholzia asprella var. longipes (Fries) P. Karsten (1882), Bidrag till kännedom af Finlands natur och folk, 37, p. 18

• Krombholzia porphyrospora (Fries) P. Karsten (1882), Bidrag till kännedom af Finlands natur och folk, 37, p. 17

• Krombholziella pseudoscaber (Secr. ex Singer) anon. ined.

• Phaeoporus porphyrosporus (Fries) Bataille (1908), Bulletin de la Société d'histoire naturelle du Doubs, 15, p. 11

• Phaeoporus porphyrosporus var. porphyrosporus (Fr. & Hök) Bataille (1908)

• Porphyrellus atrofuscus Dick and Snell, Mycologia 52:449. 1960

• Porphyrellus atrofuscus E.A. Dick & Snell (1961) [1960], Mycologia, 52(3), p. 449

• Porphyrellus porphyrosporus (Fr. & Hök) E.-J. Gilbert, (1931)

• Porphyrellus pseudoscaber Secretan ex Singer (1945), Farlowia, 2(1), p. 115

• Porphyrellus pseudoscaber subsp. cyaneocinctus Singer (1945)

• Porphyrellus pseudoscaber subsp. pseudoscaber Secr. ex Singer (1945)

• Porphyrellus pseudoscaber subsp. typicus Singer (1945)

• Porphyrellus pseudoscaber var. pseudoscaber Secr. ex Singer (1945)

• Suillus asprellus (Fries) Kuntze (1898), Revisio generum plantarum, 3, p. 535

• Suillus porphyrosporus (Fries) Kuntze (1898), Revisio generum plantarum, 3, p. 536

• Tubiporus porphyrosporus (Fries) Ricken (1918), Vademecum für pilzfreunde, Edn 1, p. 205

• Tylopilus cyaneocinctus (Singer) Grund & K.A. Harrison (1976)

• Tylopilus porphyrosporus (Fries) A.H. Smith & Thiers (1971), The Boletes of Michigan (Ann Arbor), p. 98

• Tylopilus porphyrosporus var. porphyrosporus (Fr. & Hök) A. H. Sm. & Thiers (1971)

• Tylopilus pseudoscaber (Secretan ex Singer) A.H. Smith & Thiers (1968), Mycologia, 60(4), p. 950

Photo sources:

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

Photo 2 - Author: Andreas Kunze (CC BY-SA 3.0)

Photo 3 - Author: Alan Rockefeller (CC BY-SA 3.0)

Photo 4 - Author: Missvain (CC BY-SA 4.0)

Photo 5 - Author: Dezidor (CC BY 3.0)