Yes, ferns and those kinds of cacti (as well as some others) are what I was thinking of for some basic plant shapes. Here's another that's fractal in nature:
Here's a cool page that overviews the basic cactus shapes:
http://cactiguide.com/habitsearch/
I see a lot of good shapes here that would be easy to generate with 3d fractals, and that could then cross to get interesting variants.