I am an amateur naturalist trying to discover the identity of everything that lives in my garden.
Growing on my lawn (at (1.0,1.0), see here) I found the little mushroom seen in photo 1. It's about 5cm tall with a 1.5cm diameter cap.
Unlike many of the natural history topics I'm encountering as part of my self-imposed project to identify the living things in my garden, I come to the fungi armed with a (very) little prior knowledge. Unfortunately, what my past studies have mostly taught me is that little white/brown mushrooms can be very difficult to identify! There are hundreds of species that match the description "small and whitish" and putting a name to one can be tricky, even for the experts.
Let's assume however, that you're an amateur determined to try to make progress. Where do you start? Firstly its essential you compile a detailed list of the fine features of your mushroom. Is the stem smooth or, as here (you'll need to click on the photo to enlarge) minutely powdery ('pruinose')? What colour are the gills? Do they contact the stem and run some way down it, or, as for my mushroom, are they essentially free of it? Does the flesh bruise a different colour when touched? (It didn't). And so on.
Next, its essential you take a spore print. Don't be put off - this is extremely easy to do. Simply place the cap of your mushroom, gills down, onto a sheet of paper or microscope slide, wait a while, remove and you'll find the surface has accumulated a fine dusting of spores (photo 2). Spore colour - white, black, brown (as here) or otherwise - is an extremely useful feature during identification. All good guide books include it in their descriptions.
Under a microscope incidentally, you really get an impression of just how prolific a producer of spores a mushroom really is. According to my copy of Fungi (Spooner and Roberts, Collins New Naturalist) a mushroom such as the common field mushroom (Agaricus campestris) may produce up to forty million spores an hour! Photo 3 shows a 100x close up of part of the thirty-minutes of spore production responsible for the spore print in photo 2.
Clearly you need to pick your mushroom to take a spore print. Within reason however, and provided you don't set out to decimate an area or pick especially rare species (see the list on the Fungus Conservation Forum website), this may be considered acceptable. Mushrooms themselves are basically fruit bodies. The main body of a fungus exists as a network of microscopic mycelial threads running through the soil. Picking a mushroom is analogous to picking an apple from a tree therefore (a tree with its branches running below ground and fruits popping up through the soil).
With a list of naked-eye features and a spore print, you may now be able to identify your mushroom. Unfortunately, for many species this is still not enough and further progress requires the use of a microscope (one with with a 1000x oil immersion lens).
Armed with such you can see features like those of photo 4. The blurry brown mass lower right is the edge of a gill. The brown, oval objects are spores. Spore shape and size (measured here as about 13.5um x 8.5um) varies between species and is another helpful feature for identification.
Yet another feature can be seen in photo 4 by clicking to enlarge and looking below the number '5' on the graticule. I believe (though here I am reaching the limits of my own expertise) the semi-transparent 'club shaped' entity seen there is an example of a cheilocystidium. Cheilocystidia are specialised cells that decorate the edges of the gills. Amazingly, it seems that no one really knows what they're for, but their shape and size can be yet another important diagnostic feature in your efforts to identify your mushroom.
And finally, coming back to my mushroom, what does the combination of creamy-white bell-shaped cap, cinnamon-brown gills and spore print, a fragile, pruinose stem, 13.5x8.5um oval spores and club-shaped cheilocystidia lead me to conclude about its identity ? Answer: growing on my lawn I have Conocybe siliginea...err, or possibly rickenii...or tenera...As I said, little white mushrooms are tricky!
...or possibly Concybe subovalis, which having had a few more appear on my lawn in recent days, and from the photos here, may be a good candidate.