A large amount of plant species are invasive in the southern United States. Many of them are native to moist, warm climates similar to the southern states. Invasive plants can be anything from trees to shrubs, vines, grasses, and other types of plants. These exotic plants cause problems for native plants and disrupt the ecosystem. Many were originally ornamentals that grew out of control and thrived in the new environment.
Princesstree
The Princesstree (Paulownia tomentosa), sometimes known as the Empresstree and alternately spelled Princess Tree and Empress Tree, was introduced to the United States in the 1840s. They can reach heights of 60 feet (18 meters) and 2 feet (60 centimeters) in diameter. They have large, heart-shaped leaves and showy pale-purple blooms in spring that made them attractive in landscaping. They are native to eastern Asia and are invasive not only in the south, but also the midwest and mid-Atlantic states. They grow and produce seeds very rapidly, displacing slower growing native plants and forming large groves that lack biodiversity. They are similar in appearance to various species of Catalpa.
Silverthorn
The Silverthorn (Elaeagnus pungens), or Thorny Olive, is a native shrub of China and Japan. It was brought to the United States in the 1800s as an ornamental, and it makes a fine evergreen hedge shrub in some areas, but is considered a Category II invasive plant in Florida. It is capable of hybridizing with the native Elaeagnus species there. They are a dense shrub that flowers in the cooler months from October to December. They are fast-growing and shade-, drought- and salt-tolerant, able to grow up to 25 feet (8 meters) in height if not kept in check. Sometimes they can even grow as climbing plants, and they are known for shading out other species that require sun.
Climbing Yam
Florida, Louisiana and Mississippi have all fallen victim to the Climbing Yam (Dioscorea bulbifera). It has many names, from the Chinese Yam to the Cinnamon Vine, to the more light-hearted name the Flying Potato. The Climbing Yam will infect wooded areas, wrapping around trees and shrubs, forming dense mats of vines preventing sunlight from passing, and is known to even displace native animal species dependent on plants that it destroys. They are high climbing and will go as high as 65 feet (20 meters). Once established, they are particularly hard to eradicate. They are native to Africa and parts of Asia and were introduced as a food source, not as an ornamental. They produce edible tubers, similar in appearance to small potatoes. They are presently cultivated in some locations for medicinal uses, but are out of control in the southern states mentioned.
Congograss
Described as an aggressive grass, Congograss (Imperata cylindrica) was introduced from southeast Asia to Florida, Alabama, Louisiana and Georgia in the early 1900s. It was intended to stabilize soil, but is now federally listed as a noxious weed. It resembles Johnsongrass and can grow as tall as 6 feet (150 centimeters). When it is over three feet it begins to lean and will form mats, often developing circular infestations. It is shade- and sun-tolerant, growing in open forests as well as pastures and fields. When it grows tall and begins to form mats, it prevents any other plant life from growing. Another problem it poses is that it is highly flammable and will also burn extremely hot if it catches fire.
