Frostbuster moss was a genetically-engineered form of plant lifeform, originally created for the purpose of terraforming the planet Mars. It was designed to thrive in cold conditions, and to give off greater amounts of oxygen than its natural counterparts. Frostbuster moss was also employed by Federation ecologists on planet Mestiko in the wake of "the Pulse" in order to restore that world's atmosphere. The moss was seen as a contamination of the planet by the mar-Atyya religious tradition, who tried to eradicate it during their rule of the planet between 2274 and 2282. (TOS - Mere Anarchy eBook: The Darkness Drops Again)