As advised by Lukas the main job is to find the good algorithms, if you want just perfect fins with perfect symetry simple Maths must be enough (with sinus, cosinus, some fadding …). If you want less perfect ans more nature it seems that reaction diffusion could help you, I must say directional reaction diffusion. Here an example on a sphere.
You will find examples here
Directional Reaction-Diffusion on a Cactus - Grasshopper reaction diffusion on triangular mesh - Grasshopper
And now there is also a fast implementation for GPU here