what data should we collect to have the best chance of subsequently identifying?
I'm seeing photos of fungi picked, or knocked over to see the underneath. Is this bad practice, or something we should be doing?
Good question.
Firstly, try to concentrate on good collections of more than one mushroom - This gives a good impression of variability (a single specimen may have, for example, developed abnormally).
I generally encourage people seeking an identification to turn a fruit body over by carefully digging the base of the stem up (breaking the stem or over handling sometimes causes the loss of useful features).
As long as there are several mushrooms, turning one over will have a minimal detrimental effect on the population.
The underside will give you more information than any other feature. The first thing you need to look at is the colour of the gills (if it has them) and the attachment to the stem.
If you have a camera with adjustable settings, a good depth of field is useful to capture all features in focus.
As much data as possible is preferable. It's usually possible to estimate the size from a photo (as long as there's something in the background to give a sense of scale!).
Taking note of what the fungus is growing from is very useful, e.g. soil, wood etc.
Many fungi that grow on soil are mycorrhizal species so they depend on a certain tree (or plant) to live. Taking notes of what trees are nearby increases the chances of an ID.
Also useful to give the fungus a sniff - Many have characteristic smells.
Cheers,
Nick