Spore prints

Anyone who has picked up a mushroom guide will likely be familiar with the typical use of a generalised line drawn mushroom with the different parts labelled.

This can be a useful way to summarise the key features of those fungi that fit into that type. It provides objective points to look at, describe and compare when trying to positively identify exactly which mushroom you have.

A key limitation when trying to identify mushrooms is that many species do not fit into this iconic representation, take ‘Chicken of the woods’ for example which often sprouts out of Oak trees. Even those examples that appear to resemble the above diagram may lack some of the features.

Secondly even when you do find a mushroom with the key features represented, there really is not much to analyse. I say this in comparison to plants where, generally, we have many structural features to measure, compare and describe.

Lastly, you then must compete with the fact that mushrooms will come and go as they please!

An empty lawn one day might have almost fully developed caps the following day, which might then be gone a week later. Although we can use the relationship fungi have with trees to predict where they might emerge (Fly agaric near Birch for example), they just do not stay put like plants (not including Ents).

In fact, they do stay put. Secretly meshing together the unseen world just beneath the soil, under the leaf litter, and within decaying wood. Quietly involved with a myriad of crucial ecosystem-supportive tasks, fungi are all around us.

The mushroom is the reproductive part of the species and being the only structure visible above ground is the only evidence we have for making our identification; other than the trees around where it is growing, the time of year, colour when cap is cut, associated smell, etc.

Spore prints are a fantastic addition to the mushroom identifier’s tool kit and help to provide one more piece of objective reference to compare to your field guide (if it is a good one it will describe spore colour) or smart phone app. Taking a spore print as described below is most easily achieved with any example of a mushroom you may find which has either gills or pores.

Mushrooms with gills and those with pores both drop spores from these features which then are dispersed to create more mushrooms. Your job is to capture these spores to check what colour they have. Some types of mushroom do not simply ‘drop’ spores they propel them forcefully. This difference is a broad evolutionary split, and all fungi are classified as either basidiomycetes (spore droppers) or ascomycetes (spore poppers!).

Taking a spore print
As with learning plant identification, a good start is to begin with a species you already know or have already had positively identified for you. Let us take the basidiomycete Agaricus bisporos as a species everyone is already fully familiar with.

Whether you love or hate mushrooms in your home cooking you will know this white (or brown) capped mushroom, filling the shelves in your local supermarket. Commercially distributed, it has many different common names, but you may know it as the button mushroom (in its white form) or the portobello/chestnut mushroom (in its brown form) here in the UK.

Next time you are planning a fry up leave one of the caps to one side and place it with gills facing down onto a sheet of white paper or card. You will need to slice off the stem just beneath the cap without damaging the gills.

The spores of A. bisporus are the same colour as the brown gills beneath the cap – this is best contrasted against a white surface.

Place a bowl over the top of the mushroom to create a sheltered environment for any spores to drop. Some guides encourage placing a few drops of water on the cap to encourage spore release. I only resort to this if I do not see any spores within 24 hours.

Depending on the freshness and maturity of the cap being tested you may find its spores dropping within just a few hours (very useful for in-the-field identification), but I tend to leave the cap a full 24 hours which helps to really concentrate the print. The resulting pattern is often beautiful in the case of gilled species.

Final tips and precautions
We have been looking at a known species where we expect to find dark spores (hence white paper) but spores come in a breath taking variety of colours many of which would not be contrasted against a white background.

In the field or back home after a fungi-foray you will likely have species whose spore colour you have no idea about. If this is the case remember to position your cap so that half of it sits over a white, and half over a black background. This will give you the best chance to observe the spores whatever colour they turn out to be.

If you find that you have an immature cap where the gills have not yet been exposed enough to take a spore print (common in the commercial button mushroom) you can simply slice away the edges of the cap which tend to curl beneath and hide the gills. Remember to remove the stem so that it sits easily on a flat surface.

Returning to our opening diagram it is poignant to conclude that although I have argued some of its limitations, familiarity with Image 1 is important on safety grounds. Some of the deadliest species you may encounter in the field share many of the features in that diagram. Namely these are; a bulbous base to the stem, a skirt or ring around the stem and where the gills are also white, you should be extremely carefully even in handling the mushroom.

Many mushroom pickers might only resort to taking a spore print if some niggling doubt remained in their mind after exhausting all the other observations and measurements you might take. They do however provide us with one more piece of information by which to take you from ‘’Im 95% sure this is…’’ to ‘’Okay, now I’m 100% certain this is…’’ which is always the aim when we are thinking of using fungi for our food or medicine.

I hope this has been a useful guide to taking a spore print and promotes why it is an important part of mushroom identification. If for no other reason than to enjoy the pattern it makes taking a spore print is fun, informative and often fast!