Polypore spore print tips
Like mushrooms, polypore fungi release spores from their under-surface (hymenium) that can be collected, either naturally below the fruit body or artificially on a paper or glass surface - a 'spore print'. However, there are a few tricks with polypores.
Most polypore have colourless spores, and produce a white spore print. The spore print COLOUR is therefore of limited utility for some groups (spore size, shape, ornamentation and iodine / dye reactions provide many characters, but require a high-powered compound microscope, at least 400X magnification, preferably 1000X). However in other polypore groups (especially the rusty-brown-fleshed Hymenochaetaceae, which includes Inonotus, Phellinus and their relatives) the spore print can be white, yellow or brown, and is extremely useful for distinguishing between these otherwise feature-poor fungi. So white spore deposits are useful to know, but yellow to brown is more diagnostic, as they are the more rare condition.
The first thing I do, before disturbing the fruitbody, is examine the surrounding area immediately below the pore surface to see if there is a dusting of spores. It can sometimes be on the upper surface of caps when they are shelving in layers, or on the wood closest to the base, or often on spiderweb on the underside of the fruitbody. Specimens fruiting on the underside of logs can drop their spores directly onto the soil surface. If you find such deposits, photograph it if possible, or at least make a note of it and add it to the iNaturalist post.
If there is no spore deposit and you want to try to make a spore print, the procedure is basically the same as for mushrooms: use a piece of white paper or better a glass slide (it is easier to see weak and white deposits on glass) and place the fruit body directly above it, then cover the whole thing with a cup or bowl to prevent air currents dispersing the spores - you are trying to get a good seal all around the edges. Leave it for 4-14 hours; any longer and you are likely to encourage molds. Cutting the fruit-bodies to make them fit is ok, but the less cutting the more likely it is to drop spores.
However, you must consider humidity in this process. Polypores, especially the tough ones, can dry out completely, before suddenly reviving and releasing spores - in some cases after being picked, air-dried, then re-wet months later! Conversely, sometimes they do not release spores even under seemingly optimal conditions. So if the fruitbody seems fresh and actively growing you have a reasonable chance of getting a spore print, provided you keep the fruit body moist but not wet in transit. Either collect into a fishing-tackle box, or wrap in grease-proof paper. Never put it in a zip-loc bag for more than a few minutes, as it will sweat and start to grow molds, or else start to rot. Unless it is really fresh, I recommend putting a small vial of water (e.g. an overturned bottle cap) under the covering bowl
If the fruit body is too dry, you can TRY re-moistening it in water; dunking the non-pore surface in water can help, or just drip water gradually onto the non-pore surfaces until it seems rehydrated, but NOT DRIPPING, as fungi shut down when waterlogged. Do the spore print as above, and definitely include the vial of water to maintain humidity.
If you are using paper, outline where the fruit body sat, shine incident light on the print, and change the viewing angle to visualise the spore deposit, which can be subtle.
Another very useful method, which is sometimes the only way possible: tape paper or a glass side under the fruit-body in-situ, still on its tree, leave overnight and examine the next morning. You must leave at least a small air-gap to prevent sweating and just collecting water-drops - any condensation must be able to evaporate. Sometimes it can take several days for exactly the right conditions.
If you are collecting the fruit body for a herbarium, making a spore print is VERY beneficial, because many polypores drop all their spores, leaving nothing in the fruit body, and spores can be absolutely essential for identification. So even if it doesn't seem useful, someone identifying the fungus later will be extremely grateful!
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