Well, I can give a general description of a few of them. Here's the evolutionary lines for the Mega and Mini Mushrooms.



The A. L. Nostalgium was based on the idea that it's the common Super Mushroom we know now that was the precursor to the version we see in the NES games, rather than the other way around. I'm not certain what circumstances would cause such a change.



The A. Giganticus was decided to have evolved from the A. L. Nostalgium due to the resemblance they share. My headcanon was that a population of A. L. Nostalgium was left in a place where being larger and more potent greatly increased one's chance of survival (likely Giant Land/Big Island), until these larger specimens began to spread throughout the mushroom world, albeit in fewer numbers due to the A. Giganticus taking longer to mature to spore-letting levels.



I have chosen the Smash Bros. version of the Poison Mushroom to be the base A. Toxicus because it makes the most sense, regardless of the fact that Smash Bros. probably isn't canon. It could be a variety of A. Laniatus that adapted a defense mechanism involving undeveloped spores (ones that weren't ready to be lain down to produce new A. Toxicus) being poisonous and causing the consumer to become smaller and feel weaker.



A. Vergandus, the Mini Mushroom from Mario Party 4, is believed to have evolved from A. Toxicus due to its similar effects and the somewhat-similar color scheme and effects, however the toxin produced by undeveloped spores is decreased and the fungus itself produces more Nitrous Oxide as well as minor stimulants, making the shrunken consumer feel lighter on their feet and more agile.



A. V. Novum, in my headcanon, is the result of selective cultivation of A. Vergandus. The mushrooms were encouraged to mature earlier making them easier to grow, and to produce higher concentrations of their stimulants (now identified as the agility-improving SPEED Peps), allowing the user to run faster, jump higher, and even run on water and up walls, as well as innocuously turning the pilleus blue.



What do you think?