Recent molecular studies have shown that Boletus in its current circumscription is likely an artificial grouping and it is possible that it will be split at some point into smaller genera. Note that Boletus impolitus and Boletus depilatus for practical reasons are retained here, although there is strong evidence that they are closely related to Xerocomus subtomentosus and its allies.
Fruitbody large to medium sized, boletoid, without veil and ring. Stipe solid, with surface usually covered with granules or network. Flesh variously coloured, changing or not when exposed to air. Tubes easily separable from each other, not tearing apart. Pores usually small and rounded.
Boletus immutatus (Pegler & A.E. Hills) A.E. Hills & Watling
Known to me only from the literature. Apparently very similar to Boletus luridiformis var. luridiformis, but with yellow unchanging flesh. It is also said to have facial cystidia with a long neck and blunt branches on the hyphae of the cap cuticle.
Habitat. Parkland, mycorrhizal with beech (Fagus) or oaks (Quercus).
Distribution. Currently known only from the United Kingdom.
There are no photographs available to me or hosted on the internet. Colour illustration and black and white drawings are found in Pegler & Hills (1996) and Mikšík (2010) who also provided an excellent account on this bolete.
Mikšík, M. 2010. [European species of the genus Boletus sensu stricto that do not grow in the Czech Republic III. Boletus luridiformis var. immutatus]. – Mykologický Sborník 87(3–4): 65–67 + fig. 55. (In Czech; available online on boletales.com)
Pegler, D.N. & Hills, A.E. 1996. A new variety of Boletus luridiformis. – Mycologist 10(2): 80–81.
Watling, R. 2004. New combinations in Boletaceae and Gomphidiaceae (Boletales). – Edinburgh Journal of Botany 61: 41–47.
Watling, R. & 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.