Suillellus luridus
Description
Suillellus luridus (formerly Boletus luridus) is a fungus of the family Boletaceae, found in calcareous broadleaved woodlands in Europe. Fruit bodies appear in summer and autumn and may be locally abundant. It is a firm bolete with an olive-brown cap up to 20 cm (8 in) in diameter, with small orange or red pores on the underside (yellow when young). The stout ochre stem reaches 8–14 cm (3–6 in) high and 1–3 cm (0.4–1.2 in) wide and is patterned with a red network. Like several other red-pored boletes, it stains blue when bruised or cut.
A confident identification must combine all key features: pores yellow when very young but soon become orange to red and turn dark blue/black where bruised; stem has an orange-red network pattern; when cut in half the flesh turns immediately and strongly blue but has a wine red color at the base of stem; and there is often a wine red line between the cap flesh and the pores.
Edible and good when cooked. It can cause gastric upset when eaten raw and can be confused with the poisonous Boletus satanas; as a result, some guidebooks recommend avoiding consumption altogether. When consumed with alcohol, Suillellus luridus has been implicated in causing adverse reactions similar to those caused by the compound coprine, though laboratory testing has not revealed any evidence of coprine in the mushroom.
Common names: Lurid Bolete.
Mushroom Identification
Cap
Immature specimens, such as the Lurid Bolete shown at the top of this page, are downy and pale yellow. As the fruiting body matures, the cap, which usually expands to between 8 and 14cm (exceptionally to 20cm) in diameter, becomes dull yellow-brown. The yellow cap flesh of Boletus luridus turns blue-black if it is cut or bruised. Once you cut through a cap you will see that a deep wine-colored line appears separating the pores from the rest of the cap context (the fleshy material below the surface skin) - an unusual feature in a bolete and yet another aid to identifying Boletus luridus.
Tubes and Pores
Beneath the cap, yellow spore tubes terminate in tiny circular pores that are at first yellow but eventually turn orange-red.
When cut or bruised, the tubes and pores rapidly turn blue-black before fading to pale blue.
Stem
1.5 to 4cm in diameter and 5 to 10cm tall, the underlying surface of the stem is yellow, covered with a red mesh patterning everywhere except for the top part of the stem, which remains yellow.
The swollen stem of a Lurid Bolete turns dark blue when cut and then fades back to a light blue color. The flesh near the base of the stem is deep yellow with red tinges.
Spores
Subfusiform to broadly ellipsoidal, smooth, 11–15 x 4.5–6.5µm.
Spore Print
Olive-brown.
Odor and Taste
Not distinctive.
Habitat & Ecological Role
Suillellus luridus is most commonly found under beech trees on calcareous soil. This ectomycorrhizal species is also sometimes seen beneath oak trees and very occasionally under limes. In The Burren, in southwest Ireland, I have seen Lurid Boletes growing with the lime-loving shrub Mountain Avens (Dryas octopetala), with which it is believed to form a mycorrhizal association.
Suillellus luridus Look-Alikes
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A poisonous species, has a very swollen stem covered in a deep red net pattern on a yellow background, and it has a chalky-white cap.
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Has a less swollen stem than that of Suillellus luridus, and its stem is covered in tiny red dots rather than having a reticulate (net-like) pattern on the stem as does the Lurid Bolete.
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Very similar to S. luridus and is found under the same host-trees. It produces more robust fruit bodies with a markedly tomentose cap, has a reticulum that is less pronounced and often restricted to the upper part of the stem, and is mostly found on acidic rather than calcareous soil.
Suillellus comptus
A Mediterranean bolete sharing a lot of features with S. luridus and S. queletii. This uncommon species is also found on chalky soil under oak, but generally produces more slender and dull-colored fruit bodies, with a rudimentary, incomplete, or at times completely absent reticulation, rarely extending below the top (apex) of the stem.
Suillellus queletii shares with Suillellus luridus
A vinaceous stem base and strongly bluing flesh, but completely lacks reticulation on the stem.
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Has characteristic pinkish tones in the cap and a very dense, differently patterned reticulation. When longitudinally cut, its flesh is bright yellow in the stem and stains blue only in the cap.
Suillellus hypocarycinus and Boletus subvelutipes
Can be somewhat similar, but lack reticulation on the stem.
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Can be somewhat similar, but has a more robust stem and deeper red pores.
Neoboletus sinensis
The Chinese species, originally described as a form of S. luridus but now placed in a different genus, has considerably larger spores, reported to reach 12–17 by 5.5–7 μm.
History
Suillellus luridus var. luridus was first described as Boletus luridus in 1774 by the German botanist-mycologist Jacob Christian Schaeffer, and was generally accepted by the original name that Schaeffer had given it until 2015, when other varieties of this species were formally described by Spanish mycologist J. B. Blanco-Dios; then the autonomous form took the name Suillellus luridus var. luridus (Schaeff.) Murrill after a 1909 publication by American mycologist William Alphonso Murrill (1869 - 1957).
The darker-capped (and rare in Britain) variety Suillellus luridus var. rubriceps (Maire) Blanco-Dios was first described in 1937 by the famous French mycologist René Charles Joseph Ernest Maire (1878 - 1949); it is synonymous with Tubiporus luridus var. rubriceps Maire.
Synonyms of Suillellus luridus var. luridus include Boletus luridus Schaeff., Boletus rubeolarius Bull., Leccinum luridum (Schaeff.) Gray, and Leccinum rubeolarium (Bull.) Gray.
The generic name Boletus comes from the Greek bolos, meaning 'lump of clay', while the new genus name Suillellus may perhaps imply a relationship with the genus 'Suillus' - Suillus means of pigs (swine) and is a reference to the greasy nature of the caps of fungi in that genus (but not of the genus Suillellus).
The specific epithet luridus means 'sallow' - an indefinite but unhealthy color.
Suillellus luridus Chemistry
Several carotenoids are responsible for the various colors of the cap, tubes, and stem, while variegatic and xerocomic acid cause the bluing reaction that occurs with tissue injury.
The composition of the volatile flavor compounds of Suillellus luridus consists largely of linoleic acid, with smaller proportions of 1-butanol, 3-methyl-1-butanol, pentadecanoic acid, palmitic acid, linoleic acid methyl ester, and heptadecanoic acid. Pyrazine compounds might be responsible for the characteristic odor of the dried mushroom. The predominant sterol present in the fruit bodies is ergosterol, with smaller amounts of closely related derivative compounds. The main fatty acids of the mushroom include linoleic acid (53.4% of total fatty acids), oleic acid (24.1%), and palmitic acid (10.2%). Arginine is the free amino acid found in the highest concentration (96.9 μM per gram of dry weight), followed by glutamine (9.7) and alanine (8.2).
The carotenoid content of the fruit bodies differs substantially between the cap, the tubes, and the stem. The upper part of the cap, which contains 3.1 micrograms of carotenoid per gram (µg/g) fresh weight, has predominantly mutatochrome (47% of total carotenoids), 4-keto-α-carotene (40.2%), and δ-carotene (6.4%). The major carotenoids in the tubes (totaling 4.3 µg/g) include neurosporaxanthin (31.1%), auroxanthin (17.2%), 4-keto-α-carotene (17.1%), and rhodopin (15.8%). The stem (1.2 µg/g) contains primarily auroxanthin (32.5%), followed by 4-keto-α-carotene (19.9%), β-zeacarotene (18.5%), and rhodopin (11.4%). The color change observed with tissue injury is caused by variegatic and xerocomic acids, both of which turn blue when oxidized enzymatically upon exposure to air.
Photo sources:
Photo 1 - Author: 2010-09-13_Boletus_luridus_Schaeff_104527.jpg: (CC BY-SA 3.0)
Photo 2 - Author: George Chernilevsky (Public Domain)
Photo 3 - Author: Holger Krisp (CC BY 3.0)
Photo 4 - Author: bjoerns (CC BY-SA 4.0)
