I'm going to bump up this thread again because nobody seems to recognise the significance of this Bolete growing from apparently "a concrete wall near a tube station"
This would appear to be defying science for Boletes are known to be mychorrhizal fungi (although the status of
Boletus parasitica is still being debated) - that means they will be in a 2 way relationship with the root system of a nearby tree.
So how do we explain this one then ?
Well, for starters, there is red brick inside and it looks more like a crumbling wall. It could be argued the crumbling allowed airborne organic particles to enter, but remember Boletes are mycorrhizal and the photo suggests that the emerging fungi could be responsible for forcing their way out and causing that crumbling we see.
My guess is that a tree seed fell into a crevice on the top of the wall, and sufficient nutrients had fallen into this crevice to allow the seed to germinate which in turn forced the tree to push roots down through the wall to seek water.
But Boletes are specific only to certain types of tree such as Oak, Beech, etc., so when was the last time you saw such a tree growing on a wall ?
Little Auk11 makes no mention of a tree growing nearby, so perhaps it was a very young tree - that then raises the question of how big does a tree have to be before it can produce fruiting bodies ?
Years ago, when I used to be a tree warden, I was at a conservation conference where the speaker was telling us that it is better to leave 'jagged' cuts with a chainsaw than a nice clean cut. I was mystified for as a gardener, I had always read that clean cuts are best because they heal quicker thus keeping fungal spores, etc. out.
It was then explained to me (whether true or not - I do not know) that it makes no difference as the fungal spores are already in the tree as it grows, and sometimes the spores can even be inside the seed !
(I am aware that with cultivated Truffles you have to buy the Oak already impregnated with a fungal inoculum)
One often sees Elder or Sycamore starting to grow on walls, but other trees are a lot more rare. First we have to identify the fungus, but to do this it helps to know what the tree species is, and as there seems to be no tree ............
Neil.
EDIT: I've just remembered an old article I think, by Alick Henrici, in which he asks us to keep an eye open for
B.parasiticus growing on fungi other than
Scleroderma citrinum.
Little Auk11 does mention that these were 'mini chaps' - so I wonder ?
Re: Boletus of some kind 
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