Vol 12 (3)
BOLETUS RHODOXANTHUS First authentic British record Mark Wright* Keys and images Using various keys, principally Nordic Macromycetes Vol. 2 (Hansen & Knudsen, 1992) and I Boleti (Galli, 1998) I came to the conclusion that the specimen was Boletus rhodoxanthus, the very distinct red network placing the specimen in the section Luridi. The colour changes were not quite as described in the literature: Galli describing B. rhodoxanthus as: “flesh changing only in the cap and unchanging in the stem” – my observation was two thirds of the stipe flesh changed to blue. However, Nordic Macromyetes says: “Flesh purplish red in stem base” – this agreed with the observed colours (Fig. 1). Study of the various illustrations available to me revealed that my specimen was very comparable to the second image on page 231 of Galli’s book. The first illustration on page 231 is also very similar to the photograph in Phillips (2006, p. 283).
rom Estate, Co. Fermanagh, Northern Ireland is well known as an important site for fungi with many interesting finds during the BMS foray there in 2000. Recently, at Crom on a camping trip with family and friends, I made a slight detour from one of the trails into the woods to gather what I thought was a large Agaricus. On turning it over I quickly realised it was a whitishcapped Boletus (Fig. 1) and carefully collected it for later examination – rather than ingestion! The beautiful specimen was photographed, scanned and described and the usual detective-like process of identification undertaken.
Description Pileus 9 cm in diameter, whitish grey to clay, with clay-pink tints towards the margin. Mollusc grazing damage was yellow and then pinkish; other small pinkish spots near margin were also evident. Flesh in the cap yellow, turning blue on exposure to air, A distinct reddish pink pigmented line present beneath the cuticle in cut section. Stipe 8 x 2.8–4.2 cm, covered by purplish-red net, becoming very fine at the apex (Fig. 2). Where damaged by mollusc grazing the stipe was yellow, and a yellowish colour was also evident beneath the prominent network (the net could be peeled away with fine forceps). Stipe flesh bright yellow, turning blue on exposure to air in less than 5 mins. This change reverted to pale yellow after several hours (Fig. 3). Most of the stipe turned blue except for the lower third and reddish-vinaceous tones were present in the stipe base. The flesh was fairly firm. Taste mild. Smell fruity/fungoid/pleasant. Tubes concolorous with cap flesh, also discolouring blue, 3–6 mm long, 4–5 per mm. Pores deep purple-red, concolorous with net on the stipe.
New Record A quick e-mail conversation with Geoffrey Kibby resulted in the specimen and description being sent to Kew. Geoffrey confirmed that the determination seemed highly likely with some slight reservations concerning the flesh colour changes. With these reservations in mind Geoffrey sent the photos to the Bulgarian bolete expert Boris Assyov for his opinion. Boris replied: “The photographs definitively make me think that you are absolutely right and this could not be B. rubrosanguineus, but the genuine B. rhodoxanthus. The cap of B. rhodoxanthus when young is white with some pinkish undertone as it is in your collection and it has a somewhat powdered, "farinaceous" look, which is also very well seen on the first photo. You are quite right about the bluieng flesh of the stipe, it is not common in B. rhodoxanthus but also not unheard of, moreover this specimen is young, fleshy and perfectly developed. I have sometimes observed blueing of the flesh in the upper half of the stipe in some young fruitbodies of B. rhodoxanthus and we all know that the blueing strongly depends on the water content of the fungus.
Vol 12 (3) Fig. 1. Boletus rhodoxanthus showing the intense red pigmentation contrasting with the whitish pileus. Photograph © Mark Wright.
Fig 2. Stipe detail showing the prominent red network and yellow flesh where grazed by molluscs. Photograph © Mark Wright.
Fig. 3. Cut flesh after 1 minute. Flesh (right) after several hours. Photograph © Mark Wright.
Vol 12 (3) Having in mind there is an area in the base that is not blueing at all, I would also go for B. rhodoxanthus”. [Readers who are unfamiliar with Boris Assyov’s work should go to his excellent website www.boletales.com which is a wonderful resource for the European bolete mycota with beautiful photos of most species – Editor] This species is one of a complex of very similar uncommon, mainly southern and warmth-loving species of calcareous soils, all with red pores and a red reticulation on the stipe. The best known is B. satanas, usually with a very swollen stipe, paler pores and an unpleasant smell and blueing more faintly. B. legaliae (= B. satanoides sensu auct.) (Fig. 4) has a more distinctly pinkish cap even when young and fresh, whitish flesh with an odour of chicory and is rather more common. The nearest relative of B. rhodoxanthus is probably B. rhodopurpureus, known in Britain from a few locations in Berkshire, Hampshire, and the London/Surrey border, again with more colour in the cap and blueing more strongly. There are other species described from continental Europe including the rather similar B. rubrosanguineus, seemingly restricted to conifer woods and whose white cap soon ages to become blood red.
References Galli, R. (1998). I Boleti. Edinatura. Hansen, L. and Knudsen, H. (Eds.) (1992). Nordic Macromycetes Vol. 2. Nordsvamp, Copenhagen. Phillips, R. (2006). Mushrooms. Macmillan, London.
Internet References Assyov, Boris: Boletales website http://www.boletales.com accessed 5th Dec. 2010. British Mycological Society database (FRDBI) http://www.fieldmycology.net/GBCHKLST/ gbsyns.asp?intGBNum=12513 accessed 2nd August 2010. British Mycological Society (2000) Report of Fungus Recording Excursion to Fermanagh, Northern Ireland. Northern Ireland Environment Agency Research and Development Series No. 09/01 . http://www.ni-environment.gov.uk/ fermanagh_foray_web.pdf
Full record details are: Collected from Crom Estate 2nd August 2009 in Oak/Ash/Hazel woodland above Upper Lough Erne at H35772458. One carpophore observed. Coll. Mark Wright. Det. Mark Wright. Deposited at Kew: K(M) 168614.
The photograph of B. rhodoxanthus in Phillips (2006) was taken in Corsica and the only previous British record in the BMS database lacked a voucher specimen, so this collection forms the first definite British record.
Fig. 4. Boletus legaliae with caps flushed pinkish-red and strongly blueing white flesh. Collected under oaks, Chirk Castle, Wrexham, North Wales, Aug. 2010. Photograph © Geoffrey Kibby.