Hemileccinum impolitum (Fr.) Šutara - Iodine Bolete

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

Hemileccinum impolitum, Southern Portugal

Hemileccinum impolitum, the Iodine Bolete, is a relatively rare find in Britain and far from common in the rest of Europe, where its main strongholds are in central and southern countries. Its favoured habitats are calcareous soils under broadleaf trees such as oaks.


An infrequent find in Britain and Ireland, and then mainly concentrated in southern parts, Boletus impolitus is much more common in some central and southern mainland European countries. This species also occurs in North America.

Taxonomic history

Hemileccinum impolitum was first described in 1838 by the great Swedish mycologist Elias Magnus Fries, who gave it the scientific name Boletus impolitus. The currently-accepted scientific name Xerocomellus pruinatus dates from a 2008 publication by Czech mycologist Josef Šutara, whose studied in detail morphological character os this and other closely-related boletes - since further supported by DNA studies.

Synonyms of Hemileccinum impolitum include Boletus impolitus (Fr.), Boletus suspectus Krombh., and Xerocomus impolitus (Fr.) Quél.


The old generic name Boletus comes ​​from the Greek bolos, meaning 'lump of clay', while the new genus Hemileccinum indicates .The specific epithet impolitum is a reference to the rustic, unfinished or unpolished appearance of the cap of the Iodine Bolete. Although edible, because of their rarity these boletes should not be gathered for eating.

Identification guide

Cap of Hemileccinum impolitum


Ranging from 5 to 12cm in diameter when fully expanded, the cap of Hemileccinum impolitum is clay brown to reddish beige and finely velvety at first, becoming smooth and dry except during wet weather. Young fruitbodies have rounded and domed caps, but with age they often develop slightly unevenly as though hit with a ball-pein hammer. When cut, the pale lemon-yellow flesh of Boletus impolitus may after a long delay turn faintly pink or in some instances faintly blue.

Pores of Hemileccinum impolitum

Tubes and Pores

The tubes (5 to 15mm in length) and the rounded pores ofHemileccinum impolitum are initially lemon yellow, becoming deeper yellow before with age. When cut and exposed to the air the tubes do not significantly change colour.


Closeup of the stem of Hemileccinum impolitum


The stipe of the Iodine Bolete is pale yellow, often with a red flush on its lower part, and the stem surface is granular to slightly floccose (covered in tiny fleecy or woolly scales) but never reticulate. There is a distinct iodoform odour in the lower part of the stem when it is cut or torn.

Ranging from 5 to 15 cm tall and typically 2 to 4cm in diameter, stems are usually more or less cylindrical but slightly fatter at the base.


Spores of Hemileccinum impolitum


Subfusiform, 10-16 x 4--6.5µm.

Show larger image

Spore print

Olivaceous brown.


Young specimens have a mild taste and no distinctive odour except when the lower part of the stem is cut and releases a distinctly iodoform odour.

Habitat & Ecological role

This attractive, large bolete is found most often on heavy clay soil beneath oaks and occasionally other broadleaf trees. Very occasionally on mainland Europe it appears also under conifers, and then nearly always pines.


Midsummer to the end of autumn in Britain and Ireland but sometimes continuing into the New Year in southern Europe.

Similar species

Boletus delipatus is very similar and can only be distinguished from Hemileccinum impolitum by microscopic study of the cap cuticle; Boletus delipatus is even rarer than the Iodine Bolete and is currently recorded from only one site in southern England.

Suillellus satanas has a chalky white cap, red pores and a bulbous red stem.

Caloboletus calopus has a pale cap and yellow pores; its reticulate stem is yellow near to the apex and red towards the base.

Culinary Notes

Hemileccinum impolitum is generally considered edible although hardly delectable, but because of its rarity this mushroom should not be picked for the pot.

Reference Sources

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

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.

BMS List of English Names for Fungi

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.

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