Until the turn of the present century, this untidy bolete was included within a complex of species under the scientific name Boletus chrysenteron, and so it bore the title Red Cracking Bolete. What a pity that the common name was retained by Xerocomellus chrysenteron, which rarely cracks to show the red layer just below its pelicle, while Xerocomellus cisalpinus is very good at displaying red cracks once its cap expands from convex to almost flat.
Very common throughout Britain and Ireland, Xerocomellus cisalpinus occurs also on mainland Europe and in North America.
This 'relatively new' species was first described in 2003 by Simonini, H. Ladurner & Peintner, who gave it the name Xerocomus cisalpinus. The name Xerocomellus cisalpinus is now more generally accepted and dates from a 2011 publication by German mycologist Wolfgang Klofac.
The generic name Boletus comes from the Greek bolos, meaning 'lump of clay', while the new genus name Xerocomellus indicates a (rather distant, actually) relationship with the genus Xerocomus. The prefix Xero- means dry.
The specific epithet cisalpinus is Latin and translates as 'lying on this (meaning the Roman) side of the Alps'.
Xerocomellus cisalpinus has a shallow, convex grey-yellow or brownish cap that soon crazes to reveal a thin layer of red flesh below the skin. 4 to 10cm in diameter when fully expanded, the caps have very little substance and the thin flesh blues very slightly when cut. Young specimens can have dark downy caps and might be mistaken for Bay Boletes, Boletus badius.
The tubes are yellow and usually turn slowly blue-green when cut.
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 sometimes turn greenish blue.
The stem of Xerocomellus cisalpinus, which like other Xerocomellus species has no ring, is bright yellow and the lower part is covered in coral-red fibrils. When cut or bruised, over a period of a few minutes the cream stem flesh turns blue-green near the base of the stem, where there is often a region of purplish-red stained flesh within the stem. 10 to 15mm in diameter and 4.5 to 8cm tall, the stem is more or less constant in diameter throughout its length or slightly broader at the apex. Sometimes the stem base is slightly bulbous.
Subfusiform, 11.5-14.5 x 4.3-6.8µm; very finely lined.
Habitat & Ecological role
This ectomycorrhizal species is particularly common in conifer forests, notably with spruces, but it also occurs under deciduous trees in woods and parks.
Xerocomellus cisalpinus appears in Britain and Ireland mainly from August to November, but occasional specimens can be seen much earlier in the year.
Xerocomellus chrysenteron is similar although reportedly less prone to cracking and displaying red sub-cuticle flesh; its stem base does not turn noticeably blue when cut or bruised, and its spores are not minutely striated as those of Boletus cisalpinus are.
Pseudoboletus parasiticus (synonyms Xerocomus parasiticus and Boletus parasiticus) has a yellow stem without red fibrils, and it occurs only with the Common Earthball (Scleroderma citrinum) upon which it may be slightly parasitic.
Xerocomellus cisalpinus is generally considered edible only if it is cooked thoroughly; however, it lacks both texture and flavour and so it is not rated by any but the most ravenously hungry of fungiphages.
Fascinated by Fungi, 2nd Edition, Pat O'Reilly 2016, reprinted by Coch-y-bonddu Books in 2022.
British Boletes, with keys to species, Geoffrey Kibby (self published) 3rd Edition 2012.
Dictionary of the Fungi; Paul M. Kirk, Paul F. Cannon, David W. Minter and J. A. Stalpers; CABI, 2008
BMS List of English Names for Fungi
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.
This page includes pictures kindly contributed by David Kelly.
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