U.S. Federal Definitions (Executive Order 13112):
"An alien species whose introduction does or is likely to cause economic or environmental harm or harm to human health."
"With respect to a particular ecosystem, any species, including its seeds, eggs, spores, or other biological material capable of propagating that species, that is not native to that ecosystem."
"With respect to a particular ecosystem, a species that, other than as a result of an introduction, historically occurred or currently occurs in that ecosystem."
Invasive Plant Species
"...[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. Invasive species can be plants, animals, and other organisms (e.g., microbes). Human actions are the primary means of invasive species introductions. - National Invasive Species Council
"...usually characterized by fast growth rates, high fruit production, rapid vegetative spread and efficient seed dispersal and germination. Since these plants are not native to Ohio, they lack the natural predators and diseases which would naturally control them in their native habitats. - Ohio Department of Natural Resources, Division of Natural Areas and Preserves
"Introduced species that can thrive in areas beyond their natural range of dispersal. These plants are characteristically adaptable, aggressive, and have a high reproductive capacity. Their vigor combined with a lack of natural enemies often leads to outbreak populations." - Invasivespeciesinfo.gov
Non-native Plant Species
"...those that occur outside their native ranges in a given place as a result of actions by humans. The term non-native can be used interchangeably with the terms alien, exotic, introduced, and non-indigenous... non-native plants can be thought of as those that accompany non-native peoples to a new land. - National Park Service
Alien Plant Species
"...plant species that are transported to regions outside of their natural habitat. Within a new environment, these invaders may be free of the natural controls like predators and disease that had previously regulated their population numbers. Without this control, the aliens can rapidly overpopulate an area, destroying the region's established ecological balance." - PBS Scientific American Frontiers
Exotic Plant Species
"A plant not native to the continent on which it is now found (Plants from Europe are exotic in North America; plants from North America are exotic in Japan)." - USDA, NRCS (Connecticut)
"A plant (native or non-native) that is not valued in the place where it is growing. Any plant that poses a major threat to agriculture and/or natural ecosystems within the United States." - USDA, NRCS (Connecticut)
"A plant that is particularly troublesome. Any plant or plant product that can directly or indirectly injure or cause damage to crops (including nursery stock or plant products), livestock, poultry or other interests of agriculture, irrigation, navigation, the natural resources of the United States, the public health, or the environment." - USDA, NRCS (Connecticut)
Naturalized Plant Species
"when a plant has taken over the natural range of native plants and acts like it's always been a part of the original landscape." National Park Service
"A non-native plant that does not need human help to reproduce and maintain itself over time in an area where it is not native. Even though their offspring reproduce and spread naturally (without human help), naturalized plants do not, over time, become native members of the local plant community. Many naturalized plants are found primarily near human-dominated areas." - USDA, NRCS (Connecticut)
Native Plant Species
"...one that occurs naturally in a particular region, state, ecosystem, and habitat without direct or indirect human actions." - Federal Native Plant Committee
" those that have not been introduced to a given area through the actions of humans. They are naturally adapted to their given area and they have generally existed there for much longer than have humans. The term native is often used interchangeably with indigenous. While some native species grow aggressively and can appear to invade natural areas, they are all in fact naturally adapted, and are valuable members of the ecosystem." - National Park Service
Indigenous Plant Species
"native to or occurring naturally in a particular area." - National Park Service