Red Weed

The red weed (also referred to as the red creeper or the red swamp) is a fictional plant native to Mars in the novel The War of the Worlds by H. G. Wells. It is this plant that supposedly gives Mars its dull red colour. It is one of the several types of plants brought to Earth possibly accidentally by the invading Martians, but the only one that truly was able to adapt and grow widespread on Earth. When it is exposed to water, it grows and reproduces explosively, flooding the neighboring countryside as it clogs streams and rivers. The narrator mentions near the end of "The Man on Putney Hill" that the weed glows purple at night. He tries eating some, but it has a metallic taste. Though it engulfed the native plant life of Earth it also succumbed to the effects of Earth bacteria.

Wells' earlier short story, "The Crystal Egg", features a "dense, red weed" seen on Mars that also grows heavily on water, in this case a Martian canal.

As the book has been interpreted as criticism of imperialism, the red weed could symbolize the non-native fauna colonizers introduced to the Americas, Australia, New Zealand and other countries. In many cases, these introduced species overwhelmed the native fauna, especially in remote islands.

Wells may have been influenced by the theories of Camille Flammarion, who in 1873 claimed that Mars was red due to red vegetation growing on it.