Red weed

Summary
Red weed is a red, vine like substance that spreads from where ever it's placed. The true purpose of the red weed is never clearly explained in the novel and by other following adaptations, but is often assumed to serve as a terraforming function for the occupying Martians. It is strongly debated whether the Martians intentionally planted the red weed or was accidentally spread due to the ambiguity of its purpose on earth. Despite the debate, it is certain that the red weed is the source for much of Mars’ colour. In the mod its main purpose is to be a hazard for players, causing those who come into contact with it to be slowed down and poisoned, making the killing of players easier by enemy mobs and the invading Martians.

Trivia

 * In the original novel, the red weed served as a satirical reference to British imperialism at the time, due to the fact that England had the largest empire on Earth at the time, and British soldiers being referred to as "redcoats".