At the root level mana is just mana, and animus is just animus what changes is how it binds to different substances, and raw harvested mana can have some residuals from where it was harvested. For example the pure god mana has been filtered through a lot of Illuminaries and thus purified/filtered of impurities.
Plants have animus since they are alive, therefore they can attract mana, and some plants (i.e. magical plants) have a lot of mana.
I’m not an expert, but Druids are, they harvest excess mana etc from plants and animals in a manner similar to clerics. There is some discussion of it in the Druids part of the library.
And yes on the demon human thing, it’s just how it’s constrained to the body. As Maelen notes, Edwyrd appears to be a big mana blob, not very tightly contained or controlled, something that would be very sloppy for a wizard or even another animage, symptomatic of someone very powerful, but poorly organized/disciplined/etc.