Please enjoy this blog, in which I almost convince myself I've found a bolete never-previously-recorded-in-Britain. Until I am put straight by the good people of the British Mycological Society (BMS) Facebook page...
I think I've narrowed the identification down to EITHER the common and widespread Bay Bolete Imleria badia OR (and this is my favoured option, if I'm honest) the never-previously-recorded-in-Britain Imleria heteroderma.
Here they are illustrated in Geoffrey Kibby's 'Mushrooms and Toadstools of Britain & Europe Volume 1' (2017).
So first, a confession. I don't have good notes on where this bolete was growing. We were in a rush – looking for a set of lost car keys – and I spotted this bolete which looked different to the ones I've seen before. I quickly grabbed a specimen, so I could have another go at working through the keys in Kibby's 'British Boletes' (2016).
The mushroom was growing at the edge of a conifer plantation. There were a few fruiting bodies dotted about, which I assumed to be all the same species. I selected one of the younger-looking ones to take home.
It looks like this (squares in the background are 5 mm):
The cap is orangey-brown in colour and feels like a very fine chamois leather.
Underneath the cap, the pores are cream; they don't bruise at all:
The tubes look like this in cross-section.
The stipe looks like this: concolourous but paler than the cap. It's smooth, with no discernable patterning. Although I think I can see some minute dots around the central (darker) part of the stipe.
The flesh is whitish, with absolutely no colour-change when cut.
The smell is pleasant: mushroom-y.
I've got to say – so far it's a great match for Imleria heteroderma, until you get to the bit that says:
"Under cedars in the Mediterranean, not yet British but might occur in the southern counties. Described in 1969 this species has remained almost forgotten until recently redescribed. It is close to Boletus [= Imleria] badius but differs in both colour and structure of the cap cuticle hyphae. In B. heterodermus the end cells are covered in small encrustations of plaques which stain in Congo Red dye."
Dammit. I haven't got any Congo Red dye.
Let's have a look at the cap cuticle hyphae anyway...
At 400x magnification, mounted in water, they look like this:
I am convinced I can see small crustations on those hyphae. Especially in that bottom micrograph. Although it's entirely possible what I'm seeing is dust on the lens.
I shall try and seek expert opinion!
UPDATE 09/08/2017 ~ Having received some very helpful comments from Neil Mahler and Geoffrey Kibby, over on the BMS Facebook page, it's now very clear that this bolete is the Chestnut Bolete Gyroporus castaneus.
The hollowing of the stipe is a key characteristic.
On the plus side, I was at least right about one thing: it is different to any of the boletes I've seen before.
For the record
Location: Near Spithandle Lane, Ashurst, West Sussex [private site]
Grid reference: TQ11S