Boletus truncatus (Singer, Snell & Dick) Pouzar

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

Boletus truncatus

Distribution

This mushroom is fairly common in the USA, but as far as I can tell it has not been given a common name and is not reported from Britain and Ireland.

Taxonomic history

The former Xerocomus chrysenteron group group has now been separated into several species, of which this is one.

This rather nondescript bolete is similar to Boletus chrysenteron, the Red Cracking Bolete, and these two species can only be separated with certainty by microscopic examination of the spores: Boletus truncatus spores are blunt (truncated) at one end, while the spores of Boletrus chrysenteron are round ended.

Etymology

The truncated form (ellipsoidal to fusiform but with a noticeably flattened end) of it spores are the origin of the specific epithet of this bolete.

Identification guide

Cap

4 to 10cm in diameter when fully expanded, the brownish tomentose (velvety) caps have very little substance and the thin flesh blues when cut. Caps of Boletus truncatus tend to crack as they mature, but they do not usually display pink sub-cuticle flesh

Tubes and Pores

The yellow tubes terminate in large, angular pores that are lemon yellow at first but turn greenish with age. 

When bruised, the pores of mature specimens turn dark blue very rapidly.

Stem

The stem, which has no ring, is bright yellow and the lower part is covered in coral-red fibrils that give it a 'stick of rhubarb' appearance. 10 to 15mm in diameter and 4 to 8cm tall, the stem is more or less constant in diameter throughout its length.

When cut, the cream stem flesh quickly turns blue, most notably near the base of the stem.

 

Spores

Ellipsoidal to fusiform (spindle-shaped) but with one blunt (truncated) end; 12-15 x 4.5-6μm.

Spore print

Olivaceous-brown.

Odour/taste

Not distinctive.

Habitat & Ecological role

In mixed woodland; particularly common under beech trees.

Season

August to November.

Occurrence

Probably a fairly common species in North America, but microscopic analysis is necessary to confirm its identification; not recorded in Britain.

Similar species

Boletus xerocomus, the Red Cracking Bolete, is similar but usually displays red flesh where the cap cracks; its spores have rounded ends and when bruised its pores turn blue more slowly than those of Boletus truncatus.

Culinary note

This insubstantial bolete is reported by some authorities to be edible but of mediocre quality and, like its close relative Boletus chrysenteron, often infested by maggots.

Reference Sources

Fascinated by Fungi, Pat O'Reilly 2016.

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.

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