Abundant on the well-trodden summit path, moistened by low-level clouds (and deluged by higher ones).
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.
I think you are right, though of course it will always be difficult to separate the two species until someone invents a portable t.l.c. meter.
To my mind, the 1996 paper by Moberg & Carlin gives the best advice, but infuriatingly I have mislaid my copy. (Which is why P. lambii is not yet on my website.) They carried out rather extensive correlation of morphological characters with chemistry.
Lobing of the cephalodia may not be very important.
for considering the Placopsis obervations. I have also photographed a fertile thallus that seems to want to be P. lambii, but I didn't want to overload iSpot with Placopsis.
I see there is an article in BLS Bulletin 107 from 2010. Just my luck, though - the first issue on my shelves is no. 108.
A portable TLC meter would be high on my Christmas list. If only...
In the fullness of time, past bulletins will be on the BLS website. I don't know the timescale for recent issues, though for older issues the main constraint is me! It's a job I have taken on, but other things are piling up at the moment, my being in poor health just now.
Anyhow, I didn't mention the Placopsis article as, to be honest, I didn't find it as helpful as I would hope.
Both species are well illustrated in the new Finnish lichen flora (Stenroos et al., Suomen jäkäläopas).
I am very interested in reading the older bulletins, so that is good news.
I would already own Suomen Jäkäläopas if it was in English, but as it is, I don't think I can justify the expense... yet.
You have my best wishes for a speedy recovery.
I'd like to add my best wishes too
Lat/Lng: 56.5449, -4.2212
OS grid ref: NN635414