A large bracket fungus on a mature Beech.
Caution: Do NOT use iSpot to identify fungi to eat!
Some fungi are very poisonous so a mistaken ID could have serious consequences.
No interactions present.
You say "but the way the lower surface discolours suggests G. applanatum;"
Unfortunately G australe does exactly the same. See http://www.ispot.org.uk/node/89279?nav=users_observations
Although the cross section does not show more than one years growth it does show a thick upper layer so I think G australe is likely.
Mal - I had a feeling G. australe might discolour! Thanks. I will try to get a bigger chunk the next time I go that way.
I have added a bigger cross-sectioned piece with the previous year's growth. You can see from this that the upper layer stays about the same thickness (with a bit of variation during the year) and the tube layer is noticeably thicker than it. According to Roger Phillips, this suggests G. applanatum. Just to add a bit more confusion!
The defining characteristic of the two species is that the tubes of applanatum have a sterile layer between each years growth and australe do not. Your second photo shows this perfectly so I would say you can now change the id to G australe with confidence.
Mal - Thanks, excellent detail!
Lat/Lng: 51.3683, 0.0185
OS grid ref: TQ406651