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What "Native" or "Introduced" Mean: Myths and Misconceptions

March 11th, 2025 by Alex Zorach

One of the most important aspects of our site is our classification of plants as either Native, Introduced, or Expanded in a particular region.

Unfortunately, "native" can sometimes become a bit of a buzzword. We previously wrote about common problems with nursery-grown plants which addressed some ways in which harm can come even when people buy and plant native plants. Now, we challenge other misconceptions about what it means for a plant to be native (or introduced.) Although, the general trend is that favoring native plants tends to be beneficial, there are exceptions and also other factors to consider.

Native Plants

We define a plant as native in North America if it was present at the time of European colonization. In order to make a relatively objective definition of the term "native", it is necessary to pick some sort of time cutoff. European colonization of North America was the point at which rapid changes to North America's ecosystem began, and a point after which a large number of species were introduced from other continents, so it is the best choice for a cutoff.

Why does the concept of "native" matter?

The basic idea behind native plants is that because they have been present in an ecosystem for a long time, the ecosystem has had time to adapt to their presence. Herbivores, including specialist insects, have evolved to eat the plant, and these herbivores in turn support animals higher up on the food web. Fungi and other detrivores have evolved to break down litter and dead material from the plant. Other plants have also had time to adapt to the plant's presence, tolerating things like any allelopathy (chemical inhibition of plant growth) as well as competition for light, water, and nutrients. The result is a community of organisms that is able to coexist in relative balance.

Native does not mean that a plant has always been here.

A plant that we classify as native, but is relatively new to North America in geologic time, is yellow nutsedge (Cyperus esculentus). This plant is generally thought to have colonized North America, possibly from tubers floating on ocean currents, a few thousand years ago. We consider it native because it was present at the time of European colonization.

Non-native does not mean that a plant was never here.

A plant that was once found in North America, but was locally extirpated long before European Colonization, is the dawn redwood (Metasequoia glyptostroboides). The dawn redwood, or at least trees like it, once grew across the entire northern hemisphere, evidenced by its presence in the fossil record. These trees were thought extinct, with the most recent records dating to 150 million years ago. But in the 1940's, an extant population was discovered in a remote part of China. We consider this tree non-native, even though it once occurred here, because it was not present at the time of European colonization.

Keep in mind too that saying "this plant was present in North America 150 million years ago" is an oversimplification. Speciation, the process through which plants evolve into separate species, can occur on much shorter timescales than 150 years, and we also don't know how much the historical dawn redwoods found here differed from the extant ones sourced from China. This uncertainty reinforces that "Introduced" is the correct label for such plants.

Native does not always mean good for the ecosystem.

Although in most cases, protecting native plants is a worthwhile goal, it is not always good to have a plant increase in numbers just because it is native. In some cases, human alterations to the environment can increase the numbers of a particular native plant in ways that cause catastrophic changes.

An example would be the eastern redcedar (Juniperus virginiana) in the Great Plains. Redcedars have the unusual combination of being both drought-tolerant and fire-intolerant, which naturally limited them to upland sites protected from fire, usually due to some combination of topography and soil conditions. They naturally occurred in habitats like limestone and serpentine barrens, granite outcroppings, and sandstone cliffs, where the thin, rocky soil prevented the accumulation of enough litter to cause a fire. Drier sites would have burned regularly, killing them when young, and instead supporting either open prairie (in the western portion of the Great Plains) or savanna with a mix of grasses and fire-tolerant trees such as oaks (in the eastern border of the Great Plains where they transition to the Eastern Deciduous Forests, such as the Cross Timbers region.)

Fire suppression by humans, both intentional, and unintentional through building roads which act as firebreaks, has led eastern redcedar to colonize deep-soil habitats in the Great Plain where it would not have naturally occurred. These changes can threaten grassland and savanna ecosystems and the species that depend on them.

Redcedar obviously shuts out grasses by shading them out. But it can indirectly kill even large trees. The presence of redcedar in a savanna or oak woodland provides a "ladder" through which ground fires can spread into the canopy. Redcedar also suppresses low-intensity ground fires in a normal year, which leads to greater fuel accumulation than would occur in a situation where ground fire were more frequent. The combination of greater fuel accumulation and the "fire ladder" can increase the risk of severe crown fires during prolonged droughts. These fires, which would have been rare naturally, can kill the normally fire-resistant canopy trees. They also threaten humans, as they are more likely to spread over large areas and consume homes than low-intensity ground fires that burn out quickly and are easily contained. You can read more about this dynamic in the OSU extension's article on Eastern Redcedar and Climate Change in Oklahoma’s Cross Timbers Forests.

Native does not always mean a plant supports more insects.

Although there is a strong trend that native plants tend to support far more insects than non-native ones, there are exceptions. A common example is American pokeweed (Phytolacca americana). In the eastern US, this species is the only member of Phytolaccaceae, a mostly-tropical-to-subtropical family. Among insects, it is eaten mostly by generalist herbivores, contrasting with native species such as the goldenrods (Solidago sp.) which have their center of global biodiversity here in North America, and support an extraordinary variety of insects, both specialists and generalists.

This is not to say pokeweed is bad; it supports wildlife in numerous other ways such as birds and mammals eating its fruit and seeds, and stabilizes soil in disturbed areas. And it often competes against disturbance-loving invasive plants such as common mugwort (Artemisia vulgaris) or creeping thistle (Cirsium arvense).

Introduced Plants

We consider a plant introduced if it was not present in a region at the time of European colonization of North America, and if it has become established in an area discontiguously with its native range. The most common examples of introduced plants are ones introduced from Eurasia; less commonly there are plants introduced from South or Central America into the US or Canada, or introduced across a major geographic divide between the East and West coasts.

One key reason that it is relevant whether or not a plant is introduced is that, because of the large separation from their native range, introduced plants tend not to bring specialist herbivores with them, and as such, they tend to support the food web much less than native plants. In the case of introduced plants that reproduce and grow vigorously, the lack of natural herbivores can give these plants a competitive advantage over native plants, making it more likely that they become invasive.

Introduced does not mean invasive.

A plant is said to be invasive if it establishes in a new environment where it was not naturally found, and it causes major harm to the ecosystem in that environment.

Only a small portion of introduced plants ever become invasive. In fact, an overwhelming majority of introduced plants struggle and only establish in a small region and/or specific habitats, where they are usually far from dominant. However, when introduced plants become invasive, they are much more likely to lead to collapse of the food web. Countless examples abound, some of the worst being garlic mustard (Alliaria petiolata), Norway maple (Acer platanoides), english ivy (Hedera helix), and Japanese knotweed (Reynoutria japonica).

Just because an introduced plant has not become invasive does not mean it will never become invasive.

People who rightfully recognize that most introduced plants do not become invasive often overcompensate, disregarding warranted caution in ways that leads plants to become invasive. The phenomenon of a plant becoming invasive is not always passive: active, widespread planting by humans, and breeding of new cultivars, often through combining genetic material from different source populations, which increases vigor of plants, can lead plants to become invasive.

Examples of plants that initially did not grow well in North America, but became invasive after they were widely planted include kudzu (Pueraria montana), Japanese honeysuckle (Lonicera japonica), and Lesser celandine (Ranunculus ficaria). Kudzu was widely planted in southern agriculture for years before it became invasive. Japanese honeysuckle was used both as a garden plant and widely planted to increase deer populations for hunters. Lesser celandine was widely planted as a garden plant, starting in the 1860's, valued for its pretty yellow flowers, but it did not explode in numbers until the 1990's, and even then did not reach its full extent until the 2000's or later.

The bottom line is that caution is always warranted when growing introduced plants. There is always some risk of plants becoming invasive, and this risk increases dramatically when different cultivars are being developed by breeding plants from different source populations in their native range.

Expanded Plants

"Expanded" is our novel category that we coined. It was loosely inspired by BONAP's use of the label "adventive" to describe plants native somewhere in North America but introduced elsewhere, but our term does not mean the exact same thing that BONAP does with "adventive". We say a plant is expanded if it is not native to a region, but its new range is connected to or contiguous with its native range, typically if it is separated only by smaller gaps not much larger than those that occur in its native range. The reason we use continuity, and not establishment method (i.e. garden escapes vs. natural spread) as the criterion for labeling something "expanded", is that continuity with the native range affects whether or not specialist insect herbivores are able to expand their range to find (and eat) the new populations.

As such, expanded plants function more like native plants ecologically, at least with respect to their integration into the food web. Expanded plants contrast with introduced plants, which tend to be poorly integrated into the food web.

Some examples of expanded plants include late boneset (Eupatorium serotinum), which has expanded northward, or the common sunflower (Helianthus annuus), which has expanded eastward. Numerous factors can contribute to range expansion. Global warming pushes plants northward and to higher elevations. The clearing of forests and creation of more open habitats through roads, agriculture, and creation of industrial waste ground, has created habitat for more drought-tolerant, sun-loving western plants to expand eastward.

Expanded does not mean non-invasive.

Expanded plants are much less likely to become invasive, because they bring their specialist insect herbivores with them. These insects both help to keep them in check, and ensure they support the food web. However, insect-resistance or lack of natural herbivores is only one mechanism through which invasive plants can become dominant, and collapse of the food web is only one mechanism through which they can cause harm. Thus plants that expand adjacent to their native range can still become invasive.

An example of such a plant is the black locust (Robinia pseudoacacia), widely agreed-on to be native to the Appalachians from northern AL and eastern TN, northeast through western PA and southeastern Ohio. It has, however, expanded in all directions and is now found the whole way west to the West Coast, south to the Gulf Coast, and north through New England and into Canada. The insect specialists, such as the locust borer beetle (Megacyllene robiniae), that eat it have come with it and can be found throughout its new range.

Black locust is considered invasive in New England and Canada, where it colonizes habitats which are not adapted to the presence of as large and efficient a nitrogen-fixer as it. Its presence alters these ecosystems, threatening plants adapted to lower-nitrogen conditions, and facilitating the growth of other invasive plants that are not eaten by as many insect herbivores, so it indirectly causes a similar food web collapse as species introduced from other continents. People wishing to learn more may want to read the Ecological Landscape Alliance's article on Black Locust in New England, or the Ontario Invasive Plant Council's Document on Black Locust (PDF).

Using This Knowledge as a Starting Point

We hope the takeaway here is that the labeling of a plant as native, introduced, or expanded is a key piece of information in determining the effect that plant will have on an ecosystem. But it is not a substitute for a more thorough understanding of that plant's ecology.

Using these categories is thus a useful first step or filter in choosing what to do with plants. For example, in choosing plants for a garden or ecological restoration project, it makes sense to limit your search to plants native to your local region, perhaps also considering expanded plant in some cases. However, not all of these plants will be suitable, and some of them may even be problematic plants that you want to avoid or remove for various reasons.

Similarly, if identifying volunteer plants or surveying a wild area to come up with a management plan, it makes sense to be wary of introduced plants, as any introduced plant that grows vigorously on its own is likely to be invasive. However, it is important to prioritize, and it does not always make sense to expend resources to remove plants just because they are introduced.

As we complete more plant articles, you can find more detailed information in these articles. The "control" section of articles not only gives information about how to control invasives, but also tells you scenarios where it is relatively more or less important (or even unnecessary or harmful) to control a particular species. We also want to thank our donors, small and large alike, that make the continued work on the site possible and help us to complete more of these articles.