Some plants arrive in areas where they have never been seen before, take a liking to their new lodgings, and smother out native species. It’s a bit like that distant cousin who arrives unannounced and settles in. Such super-weeds as kudzu, purple loosestrife, and water hyacinth head the list of super-villains.
The British Columbia Ministry of Agriculture and Lands doesn’t have much that’s good to say about kudzu, a vine that’s native to eastern Asia: “Kudzu is a very aggressive plant and can out-compete or eliminate native plant species thereby upsetting the natural diversity of plant and animal communities.”
The perennial plant can grow up to 30 metres (60 feet) in a year “smothering and shading plants and trees from light.”
According to the U.S. National Park Service, “Kudzu was introduced into the U.S. in 1876 at the Philadelphia Centennial Exposition, where it was promoted as a forage crop and an ornamental plant.”
According to sciencedaily.com “kudzu infests 20,000 to 30,000 square kilometres of land in the United States and costs around $500 million annually in lost cropland and control costs.” It consumes about 61,000 additional hectares each year, that amounts to an area covered by 50,000 baseball fields.
The government of Canada notes that “It grows rapidly and forms dense, ropey mats over other vegetation and structures. The plants produce massive tuberous roots, making them difficult to control or eradicate. Kudzu reduces biodiversity and causes significant productivity losses to the forestry industry.”
The botanical name is Pueraria lobata but it has gathered a number of unflattering titles as it has relentlessly progressed across the U.S. southeastern states – “foot-a-night-vine,” “mile-a-minute-vine,” “cancer of the vegetative world,” and “the plant that ate the south” are some of the milder, family-friendly ones.
The climbing and coiling plant loves a hot, humid climate. The vine has been seen in Pennsylvania and the Ohio Valley, and that is outside its normal range. In the summer of 2009, it showed up in the southwestern corner of Ontario, Canada. Kudzu doesn’t like frost much so there’s something to be said for living in a cold climate. However, global heating might change that.
It’s such an attractive plant that it’s hard to believe that water hyacinth (Eichhornia crassipes) is filled with evil intent, but it’s choking Lake Victoria in Africa.
It’s native to South America and was introduced to Africa sometime around 1879. By 1989, it had found its way into Lake Victoria and it took just seven years to clog 80 percent of Uganda’s shoreline. In its homelands, the plant is kept under control by insects that eat it, but those predators did not make the trip to Africa.
Water hyacinth plants double in area every six to 18 days, forming thick mats. France24 notes that “The plant blocks out light, dramatically reducing the amount of oxygen in the lake, and killing off fish. It also makes access to the open lake increasingly difficult for fishermen.”
But, there may be an upside. The foliage contains an unusually high level of nitrogen and carbon, making it a good candidate for being turned into a biofuel. And, its prolific growing habit means a generous supply of source material is always available.
Another attractive plant with purple flowers, a purple loosestrife plant (Lythrum salicaria) can grow up to 30 stems, producing as many as 2.7 million seeds a year.
It arrived in North America from Europe early in the 19th century, probably as seeds in soil used as ship’s ballast, or embedded in the hooves of imported cattle.
It’s fond of wetlands such as river flood planes, damp roadside ditches, and marshes, and quickly out-competes native species. Purple loosestrife is rugged; it can survive drought, changes in pH, and has adapted to the colder Canadian climate. The rascal spreads its seeds by wind, bird poop, stuck to the boots of humans or vehicle treads, and even carried around by turtles.
Purple loosestrife knows better than most plants how to colonize a region. When it sets up residence it does a lot of damage the environment that most of us may not be aware of:
Eradication is difficult. It involves pulling up plants, introducing predator insects, and spraying with herbicides. But, the New Hampshire Department of Environmental Services warns that “None of these methods will completely eliminate purple loosestrife, but they will control the populations within ecologically acceptable limits.”
Some nurseries still sell purple loosestrife as an ornamental garden plant. They should know better. However, there are many other plants we stick in our herbaceous borders that are questionable:
The list goes on and on without a mention of the bane of most gardeners―the accused dandelion.
© 2019 Rupert Taylor
Miebakagh Fiberesima from Port Harcourt, Rivers State, NIGERIA. on December 21, 2019:
Hi, Rupert, I think the main factor for this is the dispersal of the sees by air current.