Boletus pulverulentus Opat. - Inkstain Bolete

Phylum: Basidiomycota - Class: Agaricomycetes - Order: Boletales - Family: Boletaceae

Boletus pulverulentus - Blackening Bolete

Boletus pulverulentus is found under beech, lime Sweet Chestnut and oak trees, mainly in deciduous and mixed woodland but also occasionally in parkland and even in gardens. What makes this species relatively easy to identify is the instant and intense colour change of all parts of the fruitbody if handled or cut.

Distribution

In Britain this bolete is rather rare; it also occurs throughout Europe and in parts North America.

Boletus pulverulentus - Blackening Bolete, southern France

For many years in Britain this mushroom was referred to as the Blackening Bolete. In North America and latterly in Britai this edible mushroom is now referred to as the Inkstain Bolete and has this name in the BMS list of English Names of Fungi.

Taxonomic history

Boletus pulverulentus was first described in 1836 by the German mycologist Wilhelm Opatowski (1810 - 1838). Its synonyms include Xerocomus pulverulentus (Opat.) E.-J. Gilbert.

Etymology

The generic name Boletus comes ​​from the Greek bolos, meaning 'lump of clay', while the specific epithet pulverulentus means 'covered in powder' - a reference to the dry, finely velvety or slightly powdery surface of the caps and stems of young specimens.

Identification guide

Boletus pulverulentus, showing the blackening of tubes and stem

Cap

Immature specimens are finely velvety and convex, expanding to between 4 and 10cm across and becoming smooth and broadly convex but not flattening completely. The dry cap surface is a dirty dark brown, sometimes cracking and turning reddish in and around the cracks; cap surface turning black when bruised.

The yellow cap flesh of Boletus pulverulentus turns blue-black if it is cut and exposed to air.

Pores of Boletus pulverulentus, the Blackening Bolete

Tubes and Pores

Beneath the cap, yellow spore tubes terminate in large angular pores that are at first yellow (occasionally pale orange) but turn blue-black if touched. When cut or broken open, the tubes also turn blue-black.

Section of Boletus pulverulentus, showing the intense colour change on exposure to air

Stem

1 to 2.5cm in diameter and 4 to 8cm tall, the stem of a Blackening Bolete is cylindrical or slightly tapering towards the base. A brilliant yellow at the apex, the stem surface is reddish brown towards the base, and like the rest of this scruffy-looking mushroom it turns blue-black wherever it is bruised in handling.

The yellow stem flesh turns rapidly blue-black when cut and exposed to air. 

Spores of Boletus pulverulentus

Spores

Subfusiform to broadly ellipsoid, smooth, 11–14 x 4.5–6µm.

Spore print

Olive-brown.

Odour/taste

Not distinctive.

Habitat & Ecological role

Boletus pulverulentus is most commonly found under beech or oak trees, but this ectomycorrhizal species is also sometimes found under other kinds of hardwoods. Less commonly the Blackening Bolete is recorded as occurring under conifers.

Season

July to late Octobe in Britain and Irelandr.

Similar species

Neoboletus luridiformis, the Scarletina Bolete, is equally sensitive to handling and its cap, pores and red-dotted stem turn dark blue when bruised; however, its pores are red rather than yellow.

Boletus pulverulentus - Blackening Bolete,  France

Culinary Notes

You are unlikely to find enough of these often solitary boletes to justify gathering them to eat, and certainly the name Boletus pulverulentus does not appear in any of our mushroom recipe books.

Reference Sources

Fascinated by Fungi, Pat O'Reilly 2016.

BMS List of English Names for Fungi

British Boletes, with keys to species, Geoffrey Kibby (self published) 3rd Edition 2012

Roy Watling & Hills, A.E. 2005. Boletes and their allies (revised and enlarged edition), - in: Henderson, D.M., Orton, P.D. & Watling, R. [eds]. British Fungus Flora. Agarics and boleti. Vol. 1. Royal Botanic Garden, Edinburgh.

Galli, R. 1998. I Boleti. Atlante pratico-monographico per la determinazione dei boleti. Edinatura, Milano.

Dictionary of the Fungi; Paul M. Kirk, Paul F. Cannon, David W. Minter and J. A. Stalpers; CABI, 2008

Taxonomic history and synonym information on these pages is drawn from many sources but in particular from the British Mycological Society's GB Checklist of Fungi and (for basidiomycetes) on Kew's Checklist of the British & Irish Basidiomycota.

Other web pages about this species

Michael Kuo (USA)

Roger Phillips (UK)

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