Doing a bit of geocaching this afternoon I found a lot of fungi growing by a path. Most looked inedible but some were clearly of the Boletus family which includes some excellent eating varieties. The downside of them is they don't look like the sort of fungi you get prepacked on a typical supermarket shelf. Ignore the two smaller ones in the upper right, I decided they were too far gone and were probably inedible if not actually poisonous so they went in the bin immediately. Of more interest were the fat ones which had almost identical caps when viewed from the top but which looked very different underneath. As a general rule my book says avoid any Boletus with red or orange pores (the bit under the cap which are gills in normal mushrooms). So, though these two look almost identical from above they are different species I think. So, in the bin it went. Three down, one left. I cut this one in half and almost immediately the pale flesh began to turn blue. No doubt most would run a mile at this point but turning blue (the fungi not the diner ) is a good sign with some species. What I was hoping for was this fungi was Boletus appendiculatis which is rare but supposed to be excellent eating. This is yellow underneath (check) , it turns blue on cutting (check) but the cap should be a dark brown. Unfortunately, "mine" is a sickly white on top. So what is it? My best guess is Boletus albidus though it is apparently now called Caloboletus radicans. This has a pale cap and tellingly, though the flesh turns blue it quickly fades to pale again - which is what happened. It also has yellow down the stem. I think I've identified it and sadly, though not poisonous it isn't good eating being very bitter. I must keep looking.