The red weed is a plant that grows primarily on Mars and it is the plant that gives Mars its red appears. It has now made its way over to Earth when the martians invaded Earth with their tree legged/tripedal tripods and fighting machines. The red weed is a slight mixture of a slime fungus, a weed and an Ivy plant but is not exactly any of them since it is not from Earth. The red weed also glows slightly in the dark. In general, it's a bright red color.