The fungal planet type in Textures for Planets is based on two sources. First this NASA article "What Exoplanets Might Really Look Like" and of course Planet from Sid Meier's Alpha Centauri.
Here's a sample output of a Fungal planet rendered at 400x400. You can download a full 2048x2048 here.
Textures for Planets is a completely free tool for bulk rendering wrapping planet textures for your 4X or RTS space games, space scenes or art, or just for fun.