Ken Musgrave's fBm, multifractal, ridged / hybrid / hetero multifractal, functions turn out to work very well as components of a genetic texture image generating system. I inserted these five functions into my genome, modifying the code to carry the four parameters Octaves, Lacunarity, H, and Offset with each individual. The fBm nodes can appear anywhere in an image genome, hence they can nest, feeding their output into another's input x or y argument. The genetics creates arbitrary combinations of functions in Primordial Soup mode.

After scouting for some promising primordial material, you start a new seeded run and begin breeding hybrid and mutated images. Below are some examples of images containing multiple fractional Brownian motion nodes in various combinations with arithmetic and trigonometric operators. Note, these are simple image textures, not rendered in any way with geometry or lighting.

Check out Ken Musgrave's website for the best work on fractal landscapes - planets, mountain ranges, clouds, water ripples and the like. I find his chapters in "Texturing and Modeling - A Procedural Approach", 1994 Academic Press very helpful.

This page contains images with only fBm nodes and simple arithmetic operators.

fBm(multifractal (y,x),y) - a mutant	fBm(x,y) * 0.0985, another mutant	multifractal( ((HybridMF(x,y) + y) +x), y)
longish expr with 1 multifractal, 2 HybridMF's	no periodic functions, just multrifractal + 2 HybridMF'sl	fBm(RidgedMF (y,x), 0.269) -- Musgrave Agate
fBm(RidgedMF(y,x), 0.146) -- more Musgrave agate	HybridMF( RidgedMF(y,x), 0.839)	3 nested multifractals
single multifractal, Lacunarity 0.83	single Ridged multifractal	single multifractal