Rubroboletus rhodoxanthus. Found in Norfolk in mid August 2022, growing under a row of Beech trees.

Mid August 2022.

As the drought in Norfolk continued, four of us (Vanna & I and our friends Ian and James) headed out to a site some miles west of Norwich where there was still some wet ground, to look for insects and to see what plants we could find.

We were about to take a break for lunch when Vanna spotted a fungus growing beside the path under a row of Beech trees, a rather chunky bolete. We could easily have missed it altogether, as we could only see the cap from above, grey-brown in the low light beneath the trees, blending in rather well with the bare soil.

We took a closer look and realised we had found something rather special. The cap was mostly greyish-ochre but had a flush of red on its edges. The pores were red and the stem was yellow underneath a network of red veins. It was a very handsome specimen. (It was chunky too – you can see my hand holding the stipe in the photo below.)

Rubroboletus rhodoxanthus, closer up. Red pores and stem yellow underneath a network of red veins. A very handsome specimen.

Was it Rubroboletus satanas (Devil’s Bolete)? That would have been a good find, as it is quite rare in the British Isles and usually found under Beech, Oak or Hornbeam trees in the chalky parts of southern England. We needed to check. Ian took the fruitbody home and managed to identify our specimen.

Ian used “British Boletes with keys to species” by Geoffrey Kibby (note 1) to key out our beauty as Rubroboletus rhodoxanthus.

Rubroboletus rhodoxanthus

It was important to take a section through the fungus to confirm its identity: the flesh was bright yellow and stained blue only in the upper half.

Rubroboletus rhodoxanthus: sections through the stem. The flesh was bright yellow and stained blue only in the upper half. (Photo credit: Ian Senior.)

We had realised by now that we’d found something rather rare.

“British Boletes with keys to species” mentions that Rubroboletus rhodoxanthus has been found in Northern Ireland and Geoffrey Kibby’s “Mushrooms and Toadstools of Britain and Europe, Volume 1” says “rare, as yet only known from Northern Ireland, commoner on the continent” (note 2).

I posted the photographs on the British Mycological Society (BMS) Facebook page and several people confirmed the identification, including Geoffrey Kibby himself (note 3).

Our specimen appears to be the first for Norfolk and the British mainland, and with two records from Northern Ireland, only the third for the British Isles. The very first British record was from the Crom Estate in County Fermanagh in 2009 by Mark Wright, who wrote it up in Field Mycology  (note 4).

Rubroboletus rhodoxanthus was first described in 1836 and recognised as a distinct species in 1925. Until 2014 it was known as Boletus rhodoxanthus, when DNA work resulted in the splitting of Boletus into several other genera. The specific name rhodoxanthus is from rhodo- (rose) and xanthus (yellow). The fungus has been given the English name of Ruddy Bolete by the Natusfera (Spanish iNaturalist) website.

Rubroboletus rhodoxanthus forms mycorrhizal relationships with mature oak (Quercus) and beech (Fagus) trees and occasionally Sweet Chestnut (Castanea). Its distribution is concentrated in the Mediterranean region but it is found further north as well. Its worldwide range is from Morocco in the south to Norway and Sweden in the north, Spain, Portugal and the British Isles in the west and Bulgaria and parts of Russia in the east.

The fungus appears in Roger Phillips’ “Mushrooms and Other Fungi of Great Britain and Europe” (Pan Books, 1981, on page 201) as Boletus rhodoxanthus. His photo was taken in Corsica.

In Scandinavia Rubroboletus rhodoxanthus is considered to be a relict species from earlier, warmer periods and is found in open, sunny localities in broad-leaved woodlands and in tree-covered pastures and meadows (note 5).

Rubroboletus rhodoxanthus is included on the red lists of thirteen European countries. The main threat to the fungus is the loss of its host trees, through drought, pathogens and defoliation, clear felling or development. In some areas intensive trampling or damage to the leaf litter, as side effects of harvesting edible mushrooms in large quantities, could also have a detrimental effect.

Not surprisingly, much of the information on the web about Rubroboletus rhodoxanthus is from other European countries, including Italy, where the Associazione Micologica E Botanica and An Ecosustainable World (Un Mondo Ecosostenibile) websites have lots of great photos.

There are several edible and sought after boletes, such as the Cep or Penny Bun (Boletus edulis). Devil’s Bolete (Rubroboletus satanus) is a well-known exception and eating it can cause diarrhoea, stomach pains and sickness. Poisoning is quite rare, however, because mature specimens smell strongly of rotten garlic.

Rubroboletus rhodoxanthus has a pleasant, slightly fruity smell but is not considered to be edible and may cause adverse gastrointestinal symptoms if consumed. It is much to rare to consider eating anyway, especially in Northern Europe and the First Nature website gives the sound advice that “it seems sensible to leave all red-pored boletes off the menu“.

Just taking a single specimen of Rubroboletus rhodoxanthus to identify is unlikely to have much of an impact as the bulk of the fungus occurs underground as an extensive mycelium, connected to tree roots. Careful, frugal collection of specimens adds to our understanding of fungi and their distribution (note 6).

I am not announcing the exact site of our discovery to the wider world; details will be included on the record when it is submitted. But hopefully you now have an idea of the sort of habitat where you might find your very own Rubroboletus rhodoxanthus at some point in the near future.

Notes

Note 1 – The latest (8th) edition of “British Boletes with keys to species” (2017) is available to buy online from a several natural history bookshops, including NHBS, Pemberley Books and Summerfield Books. The first edition has a glowing review at Boletales.com. Highly recommended.

Note 2 – Three out of an eventual four volumes of Geoffrey Kibby’s “Mushrooms and Toadstools of Britain and Europe” have now been published. The books (over £40 each) are exquisite hardbacks full of very clear and beautiful illustrations. The illustrations for Volume 2 onwards were created digitally, using an Apple Pencil 2 on an iPad Pro. Kibby says in his Preface to Volume 2: “I think this work may have the distinction of being the first field guide produced entirely on such a device; a joy to use and much easier to edit!”

Note 3 – Thanks to everyone who helped with the identification, including several people who were familiar with this species from other parts of Europe.

Note 4 – M. A. Wright, “Boletus rhodoxanthus: First authentic British record.” Field Mycology Vol. 12, pp100 – 102 (2011). Also available as a PDF.

Note 5 – M. Andersson, T. Knutsson and M. Krikorev, “Djävulssopp, falsk djävulssopp och deras djävulskt lika dubbelgångare [The species of the genera Rubroboletus and Imperator in Scandinavia]“. Svensk Mykologisk Tidskrift Vol. 37, pp 12-25 (2016).

Note 6 – In contrast, I sometimes see whole baskets full of a mix of fungi on one of the Facebook foraging pages, posted there with the caption “are any of these edible?”.  It is good to learn about fungi but this is not the way to do it. The only sensible response is to quote the late, great Terry Pratchett: “All Fungi are edible. Some fungi are only edible once.”