Boletus calopus
Mycological characteristics
	pores on hymenium
	cap is convex
	hymenium is adnate
	stipe is bare
	spore print is olive-brown
	ecology is mycorrhizal
	edibility: inedible

Boletus calopus, commonly known as the bitter beech bolete or scarlet-stemmed bolete, is a fungus of the bolete family, found in Asia, Northern Europe and North America. Appearing in coniferous and deciduous woodland in summer and autumn, the fruit bodies are attractively coloured, with a reddish stem, yellow pores and a beige to olive cap. The bitter-tasting flesh stains blue when broken or bruised and is not edible.

Taxonomy

Described by Christian Hendrik Persoon in 1801,^[2] it derives its specific name from the Greek καλος ("pretty") and πους ("foot"), referring to its brightly coloured stalk. Its German name, Schönfußröhrling or "pretty-foot bolete" is a literal translation. An alternate common name is scarlet-stemmed bolete.^[3] The species was originally published under the name Boletus olivaceus by Jacob Christian Schäffer in 1774,^[4] but this name is unavailable for use as it was later sanctioned for another species.^[5] Johann Friedrich Gmelin's 1792 synonym Boletus lapidum^[6] is also illegitimate.^[7] Other synonyms include binomials resulting from generic transfers to Dictyopus by Lucien Quélet in 1886,^[8] and Tubiporus by René Maire in 1937.^[9] Boletus frustosus, originally published as a distinct species by Wally Snell and Esther Dick in 1941,^[10] was later described as a variety of B. calopus by Orson K. Miller and Roy Watling in 1968.^[11] Estadès and Lannoy described the variety ruforubraporus and the form ereticulatus from Europe in 2001.^[12]

Description

The yellowish pores bruise blue when injured.

Up to 15 cm (6 in) or rarely 20 cm (8 in) in diameter, the cap is beige to olive and initially almost globular before opening out to a hemispherical and then convex shape.^[13] The pore surface is initially pale yellow before deepening to an olive-yellow in maturity, and quickly turns blue when it is injured. The pores, which number one or two per millimetre, are circular when young but become more angular as the mushroom ages. The tubes are up to 2 cm (0.8 in) deep. The attractively coloured stalk, is yellow above to pink-red below, and with a straw-coloured network (reticulation). It measures 7–15 cm (2.8–5.9 in) long by 2–5 cm (0.8–2.0 in) thick, and is either fairly equal in width throughout, or thicker towards the base.^[14] The pale yellow flesh stains blue when broken, spreading out from the damaged area.^[15] The smell can be strong, and has been likened to ink.^[16] The spore print is olive to olive-brown. Spores are smooth and elliptical, measuring 13–19 by 5–6 µm.^[14]

Variety frustosus is morphologically similar to the main type, but its cap becomes areolate (marked out into small areas by cracks and crevices) in maturity. Its spores are slightly smaller too, measuring 11–15 by 4–5.5 µm.^[14]

Similar species

Boletus calopus is distinguished from edible species such as Boletus edulis by its red stalk.^[13] Large pale specimens resemble Boletus luridus, and the cap of B. satanas is a similar colour but this species has red pores. Fruit bodies in poor condition could be confused with B. chrysenteron but the stalks of latter species lack a reticulated pattern.^[15] It also resembles the similarly inedible B. radicans.^[13] Like B. calopes, the western North American species B. rubripes also has a bitter taste, similarly coloured cap, and yellowish pores that bruise blue, but it lacks reticulation on its reddish stalk.^[17]

Distribution and habitat

It grows in coniferous and deciduous woodland, often at higher altitudes, especially under beech and oak, on chalky ground from July to December, in Northern Europe,^[16] and North America's Pacific Northwest and Michigan,^[18] though the latter appears to be a different subspecies if not a separate species. In North America, its range extends south to Mexico.^[19] Variety frustosus is known from California and the Rocky Mountains of Idaho.^[14]

It has been recorded from the Black Sea region in Turkey,^[20] Yunnan Province, China,^[21] and Taiwan.^[22]

Toxicity

Boletus calopus has been reported to be eaten in far eastern Russia as well as Ukraine,^[23] yet it is regarded by most as at least inedible due to its bitter taste, or even mildly poisonous. Although it is an attractive-looking bolete, it has a very bitter taste and is not considered edible. The bitter taste does not disappear upon cooking.^[24] The bitter taste is largely due to the compound O-acetylcyclocalopin A, a δ-lactone derivative. Other compounds found in the fruit bodies include the simple lactone compound calopin,^[25] calopin B,^[26] and the novel sesquiterpenoid compounds cyclopinol^[27] and boletunones A and B.^[28] A total synthesis of calopin was reported in 2003.^[29]

See also

Fungi portal

• List of Boletus species

References