Mushrooms Which Much Logically Exist to Maintain a Biosphere can trace their origins to a population of aberrant mutant Pooplants which completely lack plastids, have converted their branches into spore-producing stalks, and specialized their roots for breaking down decomposing matter. Considering how much dead biomass regularly accumulates in the world of 2s2t, this became an easy springboard for a very prolific genus group of the diddly-darn things to arise, spreading from Oofle to Beans and Cube by way of spores riding wind currents; it took somewhat longer for viable spores to land on the irradiated continent of Dingus.
MWMLEtMaB are impressively diverse, occupying a vast array of niches, from typical decomposers, to parasites of flora and occasionally fauna, and some passively subsist on detritus. Some species employ spite in their tissues, as advertised by a display of garish colors. Species in Dingus have developed greater tolerance to the background radiation there, usually by incorporating considerable amounts of lead into their tissues. Species found in drier climates have thickened keratin cuticles, though they’re rather rare.
A species of MWMLEtMaB that has obtained enough nutrients will then fill its caps with copious spores, eventually bursting and the spores spreading to wherever the wind takes them.
Since their evolution, they have become integral in recycling essential nutrients in the ecosystems they’re found in.