shouldn't the English version read "on the tree"?
Yes, should be "on the tree". Report
Usually yes, unless they're really up in the canopy, growing on the sides of branches, but that's not usually where mushrooms grow on a tree.
Again, "on the tree". Birds can sit in the tree, but plants, mushrooms, flowers, grow ON the tree. Reported
Funny because I would have expected birds to also sit on the tree since "in" feels like inside. It just proves that prepositions are unpredictable.
This was already completed for me.
How would the sentence change if I used monia instead of monta?
The entire sentence would become "Puussa kasvaa monia pieniä sieniä". This plural partitive form refers to a larger and/or more diverse group.