This might be a dumb question, but if there is a cluster of mushrooms growing on a log, is that cluster 1 organism or multiple? I realize this question can be interpreted multiple ways, so I’ll divide it into some more distinct questions:
Does a cluster of mushrooms usually share one (dikaryotic) mycelium?
Does a cluster of mushrooms usually represent one genetic individual (i.e. Do they all have an identical gene sequence)?
For the purposes of iNaturalist, should a cluster of mushrooms be treated as a single organism?
I think there is nothing exist as dumb question so your question makes sense, I always wondered same thing, and now because of your said so ‘dumb’ question I am curious too :)
Mushrooms in a cluster are simply multiple fruiting bodies of a single organism. The particulars are slightly out of the scope of my knowledge, but generally the fruiting bodies and mycelium are genetically identical, with the exception of occasional mosaicism that I believe is described much better in this article.
For iNaturalist purposes, I personally would treat a cluster of mushrooms as a single organism, both for technical correctness and ease of use – it would get quite cumbersome to upload dozens of copies of the same image as their own observations, or take images focused on each single fruiting body you encounter.
Sure mushrooms of one species growing together are one organism, likely those 1-2 km away can be same organism too, but we just don’t know and post them separately, there’s no question like that for cluster.
A cluster of mushrooms is one organism. Because a “mushroom” is just a fruit body. The whole organism is in the substrate on which the mushroom/cluster of mushrooms grow: soil, log, etc. The analogy is the same if you asked whether several apples on the branch are many organisms or one. In the case of mushrooms you just cannot see the “apple tree”. Another analogy: for some reason you do not ask whether one thread of a mould with blue or black blob on the tip is one organism. You accept that whole cluster of mold is one organism. Same applies to the larger fungi that are called mushrooms.
A large mycelium can easily be broken apart to form multiple, disconnected mycelia. Very much like an algae that undergoes cellular division to become a long, multicellular strand that then is broken in half forming two algae. And like a jumping cholla cactus, which has lobes that are easily broken off–each of which can take root and become their own individual cacti. In each of these cases, the “pieces” of the original individual are genetically identical, but they are now separate individuals. Biologists have given these things names: the clonal colony (the collective of genetically identical individuals) is called a genet and each individual that makes up the genet is called a ramet. https://en.wikipedia.org/wiki/Clonal_colony
The colony could be formed from a single individual, but the colony could have formed due to the propagation of two genetically different individuals that happened have their spores land in the same vicinity. It’s not easy to know whether two mushrooms are connected to a single mycelium (impossible by just looking), ramets of the same genet, or multiple genets growing intermingled. So for the purpose of iNat, I’d think you can treat them however you wish.