The Chestnut Bolete, Gyroporus castaneus

 

Towards the end of the afternoon the Field Club members visiting Pilot's Wood came across a small patch of the Chestnut Bolete, Gyroporus castaneus, in amongst Sweet Chestnut mixed with Oak. This is the first time I have knowingly seen this attractive, inoffensive bolete. 

The group of Gyroporus boletes was moved into this genus sitting in its own family because of their really quite unusual cellular morphological features. This is one of two generally recognised UK species, the other being the Cornflower Bolete, Gyroporus cyanescens, a larger and chunkier bolete that is mycorrhizal with a large range of trees across its widespread range, and has flesh that blues quite intensely and quickly. 

Gyroporus castaneus is a generally light to dark brownish and relatively small bolete with white flesh, and very pleasant smell and taste. Thought to exist in Europe, North America, Asia, Africa and Australasia, in other continents it may perhaps be a species complex, based on DNA evidence. One of its stand-out features, shared with other members of its genus, is the tendency of the stem to become hollowed out, firstly in a number of separate chambers and then often completely. The cap and stipe are dry and the stipe does not have dots or a reticulum. The cap and stipe may be fairly brittle and split spontaneously. The spore colour is a straw-yellow - unusual for the Boletaceae.

The pores may darken when pressed, or with age, sometimes to quite a dark brown, but the flesh does not change colour, for example to blue, when cut. The pores are free from the stem.

Although the specific name is castaneus, the name is for the chestnut-brown colour, not its associated tree, and it is I think more generally found in mycorrhizal association with Oak. The geographical distribution covers all 4 home nations, but it is commonest in the southeast of England. 

These particular caps found in Pilot's Wood are lighter than generally expected, but within the potential range. They are mottled, partly concolourous with the stipe which is lighter in colour at the apex than the base, as quite regularly observed.

Showing the spontaneously appearing hollowed out chambers in the stipe:

 

Brown Rollrim, Paxillus involutus s. l.

 

Paxillus involutus (Batsch) Fr. is a very common and also highly toxic mushroom indeed. It'll quite likely get you in the end, destroying your red blood corpuscles after your own immune system is eventually triggered to fatally turn on you.

It is related to the poroid fruiting bodies. The gills become more pore-like as they become decurrent down the stem, and it is said that they are detachable as a layer by pushing with a finger tip at the apex of the stem. 

I couldn't really detect much downiness in either cap, although this is noted in the literature to reduce as the caps age.

Note the brown staining when handled or otherwise bruised. There is indeed a slight umbo in the shallow central depression of the cap in this quite regular cap, possibly not too old a specimen. 

In the second photo, where the cap has been turned upside down, the fluting around the edge as reported in the literature is very clear.

And another larger, somewhat more distorted (a partial rose-comb aberration perhaps?), cap nearby. 

The fluting around the rim of the cap is far more limited in extent in this specimen.

Paxillus involutus s. l. (Batsch) Fr. is a species complex of at least four species, distinguishable by DNA analysis. These fruiting bodies might be the nominate species, as they were growing in more acidic soil and close to Birch, Paxillus involutus s.s.