Alien Kudzu

""Next day, the dawn was a brilliant firey red, and I wandered through the weird and lurid landscape of another planet, for the vegetation that gives Mars its red appearance had taken root on Earth. As man had succumbed to the Martians, so our land now succumbed to the red weed. Wherever there was a stream, the red weed clung and grew with frightening voraciousness, its clawlike fronds choking the movement of the water. And then it began to creep like a slimy red animal across the land, covering field, and ditch, and tree, and hedgerow, with living scarlet feelers.""

- The Journalist, The War of the Worlds

One of the possible side-effects of an Alien Invasion.

In essence, Alien Kudzu is an alien lifeform that infests a planet's environment and begins reproducing itself rapidly. It is almost always harmful to the local habitat, whether directly (such as giving off toxic gases) or simply by outcompeting and choking out the local vegetation. It is also usually very difficult to kill, making the act of reclaiming these infestations take up great deals of time and resources (if not outright impossible).

The aliens may release it deliberately as part of their invasion in order to Terraform the Earth into a planet more suited to their own environment, or it may be just the result of the alien plants naturally being able to outproduce the local competition.

Alien Kudzu can sometimes be used for a Meat Moss effect as a sort of visual shorthand to show that things are really, really bad.

Note that neither the plant nor the invaders need to actually come from another planet; "alien" in its original sense simply refers to something foreign and/or not native. (Indeed, in Real Life this is common enough that we have a word for it -- invasive species.) They usually are, though, especially in Science Fiction settings.

Compare Explosive Breeder, which is a similar concept applied to animals. Named after the same plant as Kudzu Plot, but the two tropes are unrelated.

Anime and Manga

 * The scub coral in Eureka 7 was originally from outer space.

Comic Books

 * The League of Extraordinary Gentlemen Volume 2 deals will Wells's Martian invasion (see Literature below), and so features the red weed. In League's case it is introduced to choke off the Thames river, and so stop the movements of Captain Nemo's Nautilus, the only weapon that was having much success at all against their tripods.

Fanfiction

 * In Aeon Entelechy Evangelion Leng is a mythical plateau from the Lovecraftian Another Dimension slowly establishing its hold in our reality, starting with its ecology spreading through-out China and most of south-east Asia.

Film

 * In a segment of the 1982 film Creepshow entitled "The Lonesome Death of Jordy Verril", the titular character (played by Steven King, who wrote the original short story) discovers a newly fallen metorite. After he is contaminated with the oozing interior "meteor shit!" while trying to retreive the object, he starts to sprout a plant-like fungus which quickly spreads to much of his body. The substance also causes him to itch unbearably and even after being warned by the ghost of his father not to take a bath, he finally can no longer resist and sinks into the filthy tub. The next morning we see that the water has accelerated the growth of the fungus/alien kudzu and it now covers Jordy, farmhouse and surrounding land completely. Jordy ends his horrible ordeal with a shotgun. The segment ends with a radio weather forcast calling for extended heavy rains.
 * The story was influenced heavily by HP Lovecraft's The Colour Out of Space in which a meteorite lands in a small, backwards New England farm. The meteorite contains an alien colour which infects the land and water around the farm. Ammi Pirece, the narrator telling the story to a guy from a land development agency, states that
 * In Disney's Sleeping Beauty, Maleficent causes a wall of thorns to spring up instantly around her fortress when the Prince is trying to hack his way in.
 * Invasion of the Body Snatchers embodies this trope. That, and assimilation.
 * Dreamcatcher features a red fungus that spreads like a rash but also grows on the scenery.

Literature

 * H.G. Wells's 1898 novel The War of the Worlds is the story of a Martian invasion of Earth. As an Ur Example of this trope, the invasion sees the Red Weed spread from Mars to Earth via the Martian's ships. Growing explosively, the Red Weed annihilates other plants and chokes rivers. It increases the sense of the Earth being overwhelmed, acting as a parallel for the Martians crushing human civilization and its military. The image was used symbolically on the 2005 movie poster.
 * The Triffids from The Day of the Triffids may count. Depending on the character, interpretation and adaptation they are either an invasive alien species or genetically-modified organisms. The truth is never known for sure.
 * In David Gerrold's The War Against the Chtorr series, Red Kudzu grows extremely quickly and can cover an entire town in weeks, and it shelters predatory Chtorran life forms. Attempts to control its spread through napalm strikes are negated in days by further growth, but massive amounts of human remains have been found before it reclaims the scorched ground. All attempts to permanently destroy it have failed, and it is resistant to all known poisons.
 * The Croach in the Codex Alera.
 * Played with in Dean Koontz' The Taking. Alien fungi overrun the Earth in what appears to be a massive attempt at rapid terraforming, but then the fungi promptly vanish and everything returns to normal.
 * In Starship Troopers, the alien kudzu is from Earth; on Sanctuary, where there is almost no radiation, there is a very slow rate of mutation, so the native flora and fauna are simply overrun by Earth "more advanced" plants and animals.
 * The grey mould in Expedition Venus by Hugh Walters. In this case it's not associated with an alien invasion; it was inadvertently brought back by an unmanned space probe.
 * The Bongleweed by Helen Cresswell, a children's book about an incredibly fast-growing escapee from a botanical garden, that overruns the countryside during a heatwave.
 * Ward Moore's novel Greener Than You Think has the surface of the Earth being overwhelmed by a (human-created) variety of super-crabgrass.
 * Pandoras Star has the Primes flood the local lakes and rivers of the planets they invade with a single celled organism that is essential to their reproduction. The pollution of the waters like this kills off most of the other life in them.
 * In Harry Turtledove's Worldwar series, after humanity and the Race achieve an uneasy peace, the Race starts importing flora and fauna from their homeworld, causing ecological damage to the regions of Earth they occupy. In the final book, some white mice get (accidentally) released on the Race's homeworld and start proliferating; the Race throws a fit, completely ignoring the hypocrisy.
 * Thomas Disch's The Genocides has the Earth transformed in a monoculture for alien crops, and the aliens consider humans to be pests and try to exterminate them.

Live Action TV

 * In the Doctor Who serial "The Seeds of Death", the Ice Warriors release a fungus that multiplies rapidly and sucks the oxygen out of Earth's atmosphere.
 * In an episode of Eureka, the ice rapidly spreading over town turns out to be the result of the fungus growing in the ice.
 * In Stargate Atlantis, the base gets seeded with the material of the organic ships used by the Wraith, and Wraith ship material begins to overrun the city. Worse, it was actually growing from inside one of the main cast. (She gets better, and more importantly, )
 * Double subverted in The X-Files episode "El Mundo Gira". After a bizarre flash of lightning and hot yellow rain, an immigrant farmer is killed almost instantly by what is discovered to be a normal Earth fungus(Aspergillis) instead of an alien pathogen. However,

Tabletop Games

 * Dungeons and Dragons
 * Planescape features razorvine, growing mostly on Lower Planes, but eagerly acclimatizing anywhere. Its stem is a living razor wire, growing twisted and under tension and thus lashing around if cut. Some try to use it as a security measure, but it's a virulent weed and hard to eradicate. In some places any sod barmy enough to bring in and plant cuttings can be summarily executed. Egarus is a fungus from Abyss which was accidentally introduced on a Prime world, and after discovering that it grows everywhere and they can't even Kill It with Fire natives managed to kick it out to the Quasiplane of Vacuum... and it survives there. Egarus quietly destroys (as in, 'disintegrate') all sorts of stuff around when it can find anything.
 * Infinity Vine in Spelljammer. A leafless plant that very quickly multiplies its mass until it covers everything that got light and air with 10' thick layer (there's not enough light beyond this). Of course, if it's a ship and the extra mass is more than its power source can pull, it's stuck for good. The vine is easily destroyed, but regrows, and is immune to all diseases and poisons. Due to this magical metabolism it vanishes just as fast on planets and instantly dries up in the Flow--the only reason why the whole Prime Material Plane isn't buried under 10 feet of green ropes.
 * Warhammer 40000's Orks are a fungus-based lifeform who release spores upon death. These spores eventually mature into Orks, ensuring a planet that has been visited by Orks will always be fighting them.
 * The Tyranids also tend to infest the local ecosystem with vaguely plant-like organisms, breaking down the local biomass as one of the steps towards eating the entire planet.

Video Games

 * The creep in Starcraft, which is probably supposed to represent this (although in-game it really only affects zerg base-building).
 * Though the creep is not exactly an alien plant, but rather part of the Bizarre Alien Biology that makes up the zerg. It's closer to being zerg blood vessels than an alien plant.
 * The sequel, Starcraft II, slightly alters the way in which creep spreads, making it considerably more invasive. Though the idea was scrapped for balance purposes, creep was even originally supposed to damage non-zerg buildings over time. It remains impossible for either of the other races to build on creep, though, making this trope in full effect.
 * The Biomass in UFO: Aftermath, it's actually an attempt to build a giant psionic brain and can be driven back with special base sized psionic devices.
 * Tiberium in Command & Conquer
 * In Space Station 13 "Space Kudzu" is a plant that spreads rapidly throughout the station and can only be destroyed by fire. Fully grown Kudzu prevents anything from passing through the block that it is on.
 * Xenofungus in Sid Meier's Alpha Centauri has these properties, but doesn't exactly count since it's native to Planet. On the other hand, one could argue that the human's terraforming efforts (particularly with stands of trees) are an inversion (Earth life infesting an alien ecology).
 * Pops up in Dead Space - repurposing dead skin cells found in the dust of the ventilation system, something starts growing inside the ship, gradually transforming the atmosphere into something toxic for humans... even inside a hermetically-sealed starship, it does a lot of damage and spreads widely. On a planet, it would get out of control in short order and swallow up everything. A scientist's log specifically describes it as a "habitat adjuster" or something like that... a biological terraforming engine, in other words.
 * Star Control 2 mentions "Deep Children", modified Mycon used to terraform. They rapidly grow into lower part of crust and provoke tectonic activity until the planet is a Fire and Brimstone Hell comfortable for Mycon, but not for original species of Mycon's preferred targets--organic rich water-based worlds.
 * The Flood in Halo.
 * Systems can be found in the Space Empires series that have been infested by some sort of titanic organism.
 * Half-Life 2 has two fauna-based variations: the Antlions and the Leeches have overtaken most of Earth's landmass and oceans, respectively.
 * The body of the many in and around the Rickenbacker levels of System Shock 2
 * The enemies of Aleste and Aleste 2.
 * In Evolva, the Parasite proves to be able to fill the whole planet with its mooks. Seriously, just compare the huge number of aliens and the number of indigenes you see in each level.

Web Comics

 * This Perry Bible Fellowship strip shows one more surprisingly clingy and adaptable lifeform in this role.

Web Original

 * One of the way of terraforming planets in Orion's Arm is to release plants like this on the surface where they will progressively alter the environment to suit human life.

Western Animation
"Bombshell: You didn't tell us they bite back!"
 * The Galaxy Rangers episode "Marshmallow Trees" had shades of this, but by accident. The Kiwi ambassador was trying to share his planet's Fantastic Fruits and Vegetables with a human colony in the form of the titular trees. Unfortunately, while the trees were tested and found to be perfectly safe on Kirwin, the conditions of the colony world caused them to grow out of control.
 * Jayce and the Wheeled Warriors: The Monster Minds have vines which not only grow all over, but between planets in interstellar space.
 * Transformers Generation 1 had Morphobots, alien robotic robot-eating plants that spread quickly enough to fill an entire valley in a matter of hours, in the episode Quest For Survival. The Autobots ship them all off to a planet infested with robotic insects, after the Morphobots eat all the Insecticons' clones.

"Megatron: But those three ingrates got away!"

Truth In Television

 * The Trope Namer is kudzu, aka The Vine That Ate the South. It's an invasive species in the Southeastern United States that grows over large patches of ground, choking out native plant life by denying it sunlight and nutrients.
 * Then we have Imperata cylindrica, also known as Cogon Grass. This literal red weed chokes more acreage in the southeast than even the more infamous Kudzu and, while not quite impaction on the environment as Kudzu, it is unusually flammable.
 * So easy to grow!
 * You've got kudzu? The Soviet Union will one up you with giant hogweed, also known as Stalin's revenge! This thing is just as easy to grow, and its sap is a potent, insidious, slow-acting poison causing burns like mustard gas! It can kill kids who don't know better and tamper with it. It's also fifteen feet tall and grows in massive growths of hazardous shrubbery, like some toxic alien jungle. You have to wear a hazmat suit if you want to clear a patch of this plant monster.
 * Zucchini. They will overrun your garden if you aren't careful.
 * Caulerpa taxifolia, a type of seaweed running rampant in the Mediterranean Sea.
 * Water weed (Elodea), after its introduction in Europe and Russia was nicknamed "water plague" for its habit of growing into a sargasso in still or slow-moving waters.
 * The prickly pear cactus was this in Australia for a time. Originally introduced as an effective and self-repairing barrier for large cattle stations it eventually grew out of control and chocked off the fields it was meant to guard. It was finally brought under control by the introduction of the Cactoblastus moth which eats it (and local insect eaters will eat them just as readily as native insects).
 * Japanese Knotweed
 * Mentha spicata or spearmint is grown in pots, otherwise it does this - but underground.