|A work in progress...|
If I was trying to be super-parsimonious with this scheme, I would put druids as midway between clerics (prophets) and wizards - where witches are. But I see druids as deserving of their own slot. They're alterna-clerics, serving an older religion, more tied to nature. They also use charisma as their prime stat, unlike any other class and further distinguishing them from prophets.
How to make them more than just an outdoorsy Aquaman-type? Give them stuff they can take underground, and things they can do, and hook them up quickly with the primal elements. If they can speak to plants, why not to slime molds?
All right, so here's the basic class with a couple of variants. Basically, they can restore hit points as a cleric does (a kind of morale boost for PCs) but can't use magic to heal actual injuries at 0 hp or less.
And they get nature powers:
I'm not including these in the 52 Pages of my system just yet (the Basic-level document), but have developed them because one of our elf characters acquired an elf henchman and I was looking for ways to make this wood elf a little different in play. Hence, the powers and the classes.
Next: Two popular class/race-types I didn't put in the diagram and why not.