From the sweet scent of Honeysuckle in the heat of mid-summer to the violets of Wisteria, some of the most common and iconic plants in the Piedmont are also some of the most detrimental to their environment. What do these plants have in common that makes them so costly to their environment? Both of these, among many others, are classified as invasive species that reside in North Carolina. The United States Department of Agriculture (USDA) defines an invasive species as a species that is “non-native (or alien) to the ecosystem under consideration whose introduction causes or is likely to cause economic or environmental harm or harm to human health.” Contrary to popular belief, the terms “non-native” and “invasive” are not interchangeable. Non-native species are “plants and animals living in areas where they do not naturally exist,” and while this is true about invasive species as well, non-native species do not always cause damage to the environment.
North Carolina is home to two species included on the Federal Noxious Weed List, Hydrilla and Giant Salvinia, and three species are specific to the North Carolina Noxious Weed List, Beach Vitex, Mile-a-Minute Vine and Oriental Bittersweet. A noxious weed is “any species of plant which is, or likely to be, detrimental or destructive and difficult to control or eradicate.” Identification and methods of control are unique to each individual species, and typically the most effective way to prevent these species from causing any more damage is to stop purchasing them.
Hydrilla
Introduced to Florida in the 1950s, hydrilla (Hydrilla verticillata) quickly expanded up nearly all of the East Coast and earned itself a reputation as one of the worst aquatic weeds in the country. Multiple methods of reproduction, such as seeds, plant fragments, tubers or turion, contribute greatly to its expansion. Characterized by their pointed, bright green whorls of leaves about one to five millimeters wide and 60-20 millimeters long, hydrilla is easily confused with other, less invasive species. Their defining features, however, are white to yellowish potato-like tubers attached to the roots and white floating flowers. Hydrilla form dense layers that absorb sunlight, increase water temperature, lower dissolved oxygen levels in the water and clog lakes, rivers, reservoirs and irrigation canals.
Giant Salvinia
Giant salvinia (Salvinia molesta) was first taken out of its natural habitat by the Botany Department at the University of Colombo in Sri Lanka in 1939. Since then, the plant spread unintentionally as a hitchhiker attached to ships or as a contaminant in the shipment of other aquatic plants. The plant also travels through the natural flow of waterways and is carried by birds and aquatic mammals. Favoring warmer climates, giant salvinia has remained largely in the southeast of the United States, extending no further north than North Carolina and a few populations in Virginia. Giant salvinia is characterized as a free-flowing aquatic fern. Floating on the surface of the water, it features whorls of leaves, each two to four centimeters long and one to six centimeters wide with the upper parts of these leaves being covered with rows of white, bristly hairs (papillae). Much like hydrilla, salvinia covers the surface of water, absorbing heat and depleting dissolved oxygen. Floating mats of salvinia, up to one meter thick, impede transportation and block the flow of various bodies of water.
Beach Vitex
Nicknamed “the Kudzu of the coast,” beach vitex is a woody vine native to the Pacific rim that was introduced to the southeast United States in the 1980s. Like most other invasive species, beach vitex has many means of rapid reproduction, including relocation via animals like birds and squirrels or floating away to new beaches after being removed at high tides. A perennial shrub, beach vitex can be characterized by its oval-shaped leaves which are one to two inches in length or clusters of violet-colored flowers at the tips of branches depending on the season. Beach vitex features brittle stems that can spread more than 60 feet across the ground and branches that can grow up to two feet tall. Regarding its impact on beaches, beach vitex crowds out native dune plants such as sea oats, American beachgrass and seaside panicum. In addition, this species also poses a danger to sea turtles and their natural nesting habitat as well as rare species like the seabeach amaranth and others.
Mile-a-Minute Vine
The mile-a-minute vine was first introduced to Portland, Oregon in 1890, and in 1937 to Beltsville, Maryland, yet neither of these instances resulted in the vine making a home in America. The first case in which the mile-a-minute vine made a home was in the 1930s at a nursery site in York County, Pennsylvania. Now the vine has expanded up to 300 miles from this point of introduction. One factor that contributes to this rapid expansion is the fact that the vine can self-pollinate its seeds and disperse them accordingly. Having established its presence across the nation, the mile-a-minute vine grows rapidly, producing a thick tangle of vines over plants and scrambling up trees. These thick tangles block sunlight and limit photosynthesis which eventually kills covered plants. The mile-a-minute vine can be characterized by alternating pale green leaves, delicate stems with recursive barbs, ocrea surrounding the base and small, white flowers.
Oriental Bittersweet
Not only do many see it as one of the most visually appealing species on the NCNWL, the oriental bittersweet is also one of the oldest species. Introduced to the United States for the first time in the 1860s, the vine has since gained a reputation for being extremely aggressive and damaging. Similar to other vines, oriental bittersweet largely relies on birds to distribute its seeds to reproduce, though it can also reproduce asexually by sprouting from its root system. Able to climb up to 60 feet in height, oriental bittersweet is best categorized by its alternate, toothy leaves, brown, multi-branched vines and, depending on the season, either green or red to yellow fruits. While it shares similarities to the American bittersweet, this species has elliptical leaves, and its fruits and flowers occur in a single clump at the end of a branch, rather than throughout. Much like the mile-a-minute vine, oriental bittersweet poses a threat to its environment based on the fact that it overgrows all other native species and weighs down on the canopies of trees.
From the beach vitex of the North Carolinian coast to the oriental bittersweet found in the mountains, North Carolina is home to its fair share of invasive species. As with many invasive species around the world, these tend to pose threats to the native flora and fauna of the environment they have found themselves in.
