Many spells, such as Fox's Cunning, apply to "creatures". There are "mundane" plants and "monster" plants. Which count as creatures for the purposes of these kinds of spells?
Paizo's page describing creature types (link) has the following for plants (truncated):
This type comprises vegetable creatures. Note that regular plants, such as one finds growing in gardens and fields, lack Wisdom and Charisma scores and are not creatures, but objects, even though they are alive.
So nope, not all plants count as creatures. Ordinary plants are not creatures and cannot be targeted by such spells.