I'm writing up an NPC (partly for my campaign, partly for submission to this fantabulous site) and I've run into a problem: this character, though originally conceived as a druid, doesn't actually fit into the 3.x paradigm of "druidicness". Druids in D&D are representatives of nature as a whole; this character speaks only for the plants. As such, a number of the canon druidic powers are inappropriate and should be replaced by different skills, feats and (potentially) spells.
The question is this: should I write up a new base class -- and I'd want it to be a base class, not a prestige class -- to do this? Instead of hacking the druid class, should I make him a cleric with a single domain (Plant) and no god? Or should I just call him a druid anyway and then stat him completely differently (which is what I've done now)? I hadn't realized how confining the existing paradigms were so I'm somewhat at a loss.
If it is for an NPC, I would either hack up the Druid or just have him be selective about what he takes, can do, etc. I don't see a ton of reason to make a whole new class for what is essentially a single persona. Now it still might be fun to do and share.
I think either a new base class or a variant on the existing Druid would work. It really depends on how much change you need. If you need to call out exceptions on every/most levels and/or you have so many exceptions to the spell list, you might as well make a new spell list. If you can do it in a short amount of space, do it. "Replace ability X with Y, remove Z, and only take spells with the Blah descriptor.." Unearthed Arcana has a bunch of variants on base classes. They are all done in about a paragraph of text.
Back to the Cleric vs Druid part. It really depends on whether he speaks for the plants, or with/from/through the plants. He could be a cleric and obtain spells through what is essentially a deity, but is not what we would typically ascribe to be a deity. Maybe the deity is really the pinnacle of an awakened plant. There are other options. If there can be entire demi-planes composed of sentient organisms, there can be the essense-of-plant-become-sentient.
I also don't think that only caring for plants really goes against being a druid. It isn't typical, but it is still being a protector and champion for an aspect of nature.
*shrug* IMHO, of course.