General Topics

Invasive Plants of Missouri

What is an Invasive Species?

In order to fully understand that question, it is helpful to first learn about native species. By definition, a native species is any species that is living in its historical range, usually where that species has lived for thousands or even millions of years. For various reasons, overtime, humans have moved species around the world. People have introduced many different species — plants, animals, etc. to new ecosystems. These displaced species are commonly referred to as alien or exotic species. Alien species are species that live outside of their historical range. These alien species are different than invasive species. When an alien species is first introduced to a new environment, there are often not any natural enemies of that specific species in the new ecosystem. As a result, the population of that specific alien species could grow out of control and wreck havoc on that ecosystem. An alien species can become classified as an invasive species when it starts to cause harm to the environment, though not all alien species are invasive and threaten biodiversity. By definition, an invasive species is any non-native species that can cause serious harm to an ecosystem. So far, there are about 50,000 non native species currently in the United States. Of that number, about 4,300 of those species are classified as invasive.

​Invasive species were sometimes introduced to the United States intentionally, but most of the times, the species arrived unintentionally. When people were first populating the country, they brought many plants to use as decorations. These decorative plants ended up becoming invasive and killed the native plants. Some plants were introduced to the United States through the nursery trade hidden in other vegetation. When species come to the United States without humans knowing, they are known as unintentional introduction (fws.gov). In addition, invasive species often formed groups that spread in different ways. Each group of invasive species is conneected with a certain historical time period and certian ecological trait. Species that are found all over the world or all over a country have been found to be habitat generalists that spread before World War I (Bertelsmeier et al).

Characteristics of Invasive Species

Invasive species have many characteristics that help them overtake native species in their new locations. Invasive species tend to have very few predators in their new environment. Since they originated elsewhere, when they are first brought over to the new area, there are not any predators adapted to kill the invasive species. As a result, these invasive species are able to grow out of control because there aren’t any predators to keep their population in check. In addition, invasive species are able to grow their population relatively quickly. They are able to reproduce quickly and can produce many offspring during each cycle. Also, invasive species have many methods of dispersing their seeds. They are not limited to just one way of dispersal — for instance, invasive plants can spread their seeds through the wind or through animal scat. Invasive species tend to be generalists, meaning that they do not have very specific food sources or environments. They are able to survive, and even thrive, in many different types of environments.

Impacts of Invasive Species

As mentioned above, invasive species negatively impact the surrounding environment. Some consequences of invasive species include a decrease in plant diversity, greater amounts of soil erosion, decreased water quality, agricultural lands that are no longer rich in nutrients and a decrease in the amount of native plant species. In particular, invasive plants have led to a decrease in the number of endangered and threatened species in the United States (United States Department of Agriculture). Invasive species are able to change the nature of the environment that they are invading. For instance, they are able to disrupt the number of native species, the local ecology of the environment, the food chain, and they can ultimately cause the extinction of the native species. In addition to harming the environment, invasive species can negatively impact human health. They can carry diseases or contain poisons. About half of the poisonous plants in the eastern U.S. are non-native and many of them are considered invasive (fws.gov). One specific impact of invasive species includes the ability to change pollinator biodiversity and alter the services the pollinators are able to provide to the ecosystem (Vanbergen et al). But studies have found that it is very difficult to predict the outcome of introducing a species to a new environment — it can be challenging to determine how the invasive species will interact with the native species. The short-term consequences of invasive species can be difficult to determine immediately (Buckley).

Control of Invasive Species

It can be very difficult to control the spread of invasive species. But if you act quickly after the species has been introduced, there is a chance you can eradicate it. Most of the time, you will just have to manage the spread of the species from taking over more land and killing more native species. One method of control is through physical or mechanical control. This involves cutting down the invasive plant and physically getting rid of the plant and using physical barriers to control the areas where the plant can grow. In this case, humans are physically intervening with the growth and spreading ability of the invasive species. Another type of control is known as chemical control. This is when humans use pesticides or any chemical in general to try and kill the invasive plants (fws.org).

Common Invasive Plants in Missouri

 This guide will introduce you to many different invasive trees and shrubs that are commonly found in Missouri. The following is not an exhaustive list of all of the invasive plants, just the few most common that you are likely to find on your way to school or walking around your neighborhood.  I highlighted these couple of species because they are very common throughout the entire state and are commonly found in your backyard or in front of your work or school.  

Callery Pear (Bradford Pear)

Scientific Name: Pyrus Calleryana

Origin: China and Vietnam

Background/Introduction to the United States:

  • First introduced in Massachusetts in 1908
  • Originally used for ornamental landscape plantings
  • Fruit industry used the callery pear fruits as root stock for commercial pears

Identification/Description:

  • Deciduous tree that is about 30-50 feet tall with wide branches
  • Five petaled white flowers that occur in the spring
  • White flowers that bloom in the spring that grow in clusters
  • Five-petaled flowers that are 1/2 to 3/4 inches across
  • Grows fast
  • Small spherical fruits that are green and brown in color
  • Fruits start growing once the tree is at least three years old
  • Alternating leaves along the stem
  • Leaves are heart-shaped/shaped like ovals with toothed edges
  • Leaves turn red/purple in the fall
  • Trees grow in the shape of a cone
  • On younger trees, the bark is smooth and a brownish-red in color
  • Bark changes to a gray brown as tree ages
  • Branches contain thorns

Habitat:

  • Found in disturbed woodlands, along roadsides, and in old fields
  • Trees spread fast in temperate climates
  • Can tolerate different soil types

Threats to the Environment:

  • Seeds can spread very quickly and overtake areas
  • Creates dense thickets that make it difficult for native plants to grow
  • Leafs out earlier than native trees in Missouri — leads to a decrease in the amount of sunlight reaching spring wildflowers
  • Creates dense, thorny thickets that make it difficult for native species to colonize that specifc area
  • Ice and storms can easily break weak branches that easily break — branches can damage cars or anything located underneath it when the branch breaks

Oriental Bittersweet

Scientific Name: Celastrus Orbiculatus

Origin: Native to temperate Japan, China and Korea

Background/Introduction to the United States:

  • Came to North America as an ornamental vine around 1860
  • Fruits can be used in wreaths and dried flower arrangements
  • Used to help control erosion along highways

Identification/Description:

  • Oriental Bittersweet is a leafy, deciduous vine
  • Produces green fruits in the summer that turn bright yellow/orange in the fall — the outer membrane of the fruit splits open in September to show a bright red inner fruit that contains 1 to 2 seeds
  • Fruits grow in clusters of 1 to 3 and attach to the vine at the leaf axial on the stem
  • Vines can reach heights of over 60 feet and move around trunks and branches of other trees
  • Stems can be up to 4 inches thick
  • Brown twigs and branches with tan lenticels (raised pores/bumps that help the twigs and branches with the process of gas exchange with the atmosphere)
  • Alternating leaves that are round with toothed edges and about 2 to 5 inches long — leaves are glossy green in the spring and turn golden yellow in the fall
  • Green/yellow five-petaled flowers bloom in the leaf axils in the spring — flowers are located in small clusters of three to seven

Habitat:

  • Found along the edges of forests/woods and in gaps in the forest
  • Old fields
  • Coastal areas
  • Roadsides
  • Grasslands
  • Beaches
  • Seeds germinate best in environments with little light

Threats to the Environment:

  • Vine is able to grow rapidly and overtops trees — cuts the trees off from sunlight causing them to die — the vine can then take over the space of the tree
  • Leaf litter contains a large amount of calcium and ends up increasing the soil pH — makes it difficult for the other plant species to survive
  • Birds are able to eat the fruits and disperse the seeds to other areas allowing Oriental Bittersweet to take over more land
  • Vine can wrap itself tightly around shrubs and trees and constrict those trees and shrubs
  • Oriental Bittersweet is able to hybridize with American Bittersweet — could end up potentially threatening the genetic identity of the American Bittersweet

Burning Bush

Scientific Name: Euonymus Alatus

Origin: Northeastern Asia, Eastern Russia, China, Japan, Korea

Background/Introduction to the United States:

  • Came to the United States in the 1860s from northeastern Asia as an ornamental plant
  • Popular in landscaping

Identification/Description:

  • Name comes from the bright red appearance of the leaves in the fall
  • Deciduous shrubs
  • Leaves are typically less than 2 inches long and grow opposite along the stem
  • Leaves are shaped like an ellipse coming to a narrow point on both ends and have very fine “teeth” on the edges
  • Flowers bloom in the spring and lay flat against the leaves
  • Each flower is green/yellow in color and has four petals
  • Smooth red/purple fruits with orange seeds mature by the end of summer
  • Bushes can grow to be 12 feet in width as a result of long branches and can reach heights of 20 feet
  • Winged branches

Habitat:

  • Can grow in many different types of soil
  • Tolerant to shade
  • open wood
  • pieces of land that have previously been disturbed
  • floodplains
  • Areas that are in the very beginning stage of forest growth

Threats to the Environment:

  • Can create dense areas/thickets that are able to overtake other understory plants for light and space and displace the plant species that are already living in that location
  • overtakes native species
  • Can invade many different habitats
  • Animals and birds eat the seeds which helps to disperse the shrub to other locations

Winter Creeper

Scientific Name: Euonymus Fortunei

Origin: Japan, Korea, China

Background/Introduction to the United States:

  • Came to the United States from China in 1907 as an ornamental ground cover plant

Identification/Description:

  • Perennial evergreen vine
  • Grows as a climbing vine or a vining shrub if there is nothing for the Winter Creeper to climb
  • Climbing vines can reach a height of 40 to 70 feet
  • Glossy green egg-shaped leaves with fine teeth along the edges or wavy edges that grow opposite each other along the vine
  • Leaves are less than one inch long and often have white or off-white veins
  • Contains 1/4 inch long flowers that are five-petaled and greenish white in color that bloom during the middle of the summer
  • In the fall, the flowers turn pinkish red in color
  • Contains spherical and smooth fruits that are pinkish-red in color with orange seeds which grow from September to November
  • Flowers and fruits typically only grow on the vines that are able to climb
  • Aggressive and rapidly growing perennial woody vine
  • Produces rootlets which are small roots that can end up forming new plants

Habitat:

  • Can tolerate many conditions
  • Tolerates a lot of shade or a lot of sun
  • Grows in forests and gaps in the forest
  • Can tolerate soil that is rich or poor in nutrients and has a basic or acidic pH — prefers soil that is drier
  • Drought tolerant

Threats to the Environment:

  • Grows in very dense bunches that make it difficult for native plants to grow
  • Climbing vines kill shrubs and trees
  • Animals and birds eat the seeds which helps the vine spread to new locations
  • Climbs on rocks and trees and spreads over the ground causing the native plants to die
  • Grows rapidly and eliminates ground space for other native plants to grow
  • Out competes native plants for space, sunlight and nutrients

Amur/Shrub Honeysuckle

Scientific Name: Lonicera Maackii

Origin: Eastern Asia, Central and Northeastern China, Manchuria, Korea

Background/Introduction to the United States:

  • Brought to the United States because of the attractive flowers
  • U.S. Department of Agriculture uses it as a wildlife cover and to help control erosion
  • Commercial nurseries use it as an ornamental

Identification/Description:

  • Deciduous shrub
  • Contain opposite leaves that end in a long point and are one to two and a half inches long
  • Contain flowers that begin as whit in color and transition to pink and then fade to yellow
  • Produce red berries
  • Can grow up to 15 to 20 feet in height
  • Blooms from May to June
  • Grayish brown bark that his broad ridges and grooves

Habitat:

  • Old Forests
  • Forest edges
  • Thickets
  • Floodplains
  • Maritime forests
  • Tolerant of shade, sun/light, and wet and dry locations
  • Understory shrub
  • Tolerates many habitats

Threats to the Environment:

  • Grow leaves earlier in the spring than the native species and hold their leaves longer than other species giving them a competitive advantage — steal light from native plants
  • Honeysuckles make it difficult for forests to regrow because there is less room for the native species — causes species richness in forests to decrease
  • Birds and animals eat the berries and disperse the seeds in new locations allowing the shrub to spread

Tree of Heaven

Scientific Name: Ailanthus Altissima

Origin: Northeastern and Central China and Taiwan

Background/Introduction to the United States:

  • Introduced to Philadelphia in 1748
  • Thought to be a possible food plant for the silkworm industry
  • Name comes from the ability to grow out of rocks on mountains — could reach heights greater than the other trees
  • Nurseries sold the tree because it did not contain any pests, grew relatively fast, and could tolerate different soil types
  • Chinese immigrants brought Tree of Heaven seed to the West Coast during the Gold Rush in the 1850s for medicinal reasons

Identification/Description:

  • Deciduous tree with alternating compound leaves
  • Has yellow-green flowers that are present during June
  • Brittle wood
  • Fast Growing
  • Can reach heights of 80 feet or more
  • Contains 11 to 41 leaflets on a straight stem that are part of a large one to four feet long compound leaf — appears during late spring
  • Leaflet is lance shaped with a long tip — there are one to five teeth at the base of the leaflet
  • Leaves are alternating
  • Leaflets are opposite each other
  • Crumbled leaves release an odor similar to old peanut butter
  • Smooth bark that is light brown or grayish brown
  • Produce yellow flowers that are located in clusters above the leaves near the end of the branches
  • Male and Female trees are different
  • Female tree produces tan seeds in the late summer to fall

Habitat:

  • Found in at least 30 states in the continental United States and Hawaii
  • Tolerates a large range of soil types and conditions — tolerates acidic soils
  • Prefers full sunlight — not very tolerant to shade
  • Tolerant of drought
  • Can adapt well to many different disturbances –thrives in disturbed areas
  • Can withstand air pollution
  • Found in urban areas
  • Can grow in garbage, between stones by rail lines, pavement cracks, vacant lots, sides of highways, field edges, urban pavement cracks, railroad beds, mine soils, disturbed forests

Threats to the Environment: 

  • ​Can damage sewers, pavements and infrastructures if located near places with human development
  • ​Creates dense stands and takes up lots of space — leaves very little room for native plant spieces to grow
  • ​Contains chemicals that are leeched into the soil — those chemicals act as herbicides and impair the growth of the surrounding plants — makes it easy for Tree of Heaven to take over land and spread
  • ​Can regrow once it has been cut down — very hard to eliminate

Sources:

https://mdc.mo.gov/sites/default/files/resources/2012/05/callerypearinvasive.pdf

https://www.invasive.org/101/moreinfo.cfm

https://oceanservice.noaa.gov/facts/invasive.html

https://www.nps.gov/plants/alien/pubs/midatlantic/aial.htm

https://nature.mdc.mo.gov/discover-nature/field-guide/tree-heaven

https://www.invasiveplantatlas.org/subject.html?sub=3023

https://www.na.fs.fed.us/spfo/invasiveplants/factsheets/pdf/oriental-bittersweet.pdf

https://mdc.mo.gov/trees-plants/problem-plant-control/invasive-plants/wintercreeper-control

https://mdc.mo.gov/sites/default/files/downloads/WinterCreeper.pdf

http://www.missouribotanicalgarden.org/PlantFinder/PlantFinderDetails.aspx?kempercode=d617

https://nature.mdc.mo.gov/discover-nature/field-guide/bush-honeysuckles

https://nature.mdc.mo.gov/discover-nature/field-guide/callery-pear-bradford-pear

Kaufman, Sylvan Ramsey., and Wallace Kaufman. Invasive Plants: A Guide to Identification, Impacts, and Control of Common North American Species. Mechanicsburg, PA: Stackpole, 2013. Print.

Vanbergen, Adam J., Anahí Espíndola, and Marcelo A. Aizen. “Risks to Pollinators and Pollination from Invasive Alien Species.” Nature Ecology & Evolution 2, no. 1 (January 1, 2018): 16–25. https://doi.org/10.1038/s41559-017-0412-3.

Bertelsmeier, Cleo, Sébastien Ollier, Andrew Liebhold, and Laurent Keller. “Recent Human History Governs Global Ant Invasion Dynamics.” Nature Ecology &Amp; Evolution 1 (June 22, 2017): 0184.

Buckley, Yvonne M. “Invasion Ecology: Unpredictable Arms Race in a Jam Jar.” Nature Ecology &Amp; Evolution 1 (January 4, 2017): 0028.

https://www.fws.gov/invasives/faq.html

 ​Callery Pear tree used for decoration along the side of a road

Image Source: Lucy Cohen

Oriental Bittersweet vine wrapped around a tree in Powder Valley Nature Center in St. Louis

Image Soure: Lucy Cohen

Close up of Oriental Bittersweet vine in St. Louis

Image Source: Lucy Cohen

Burning Bush during the winter

Image Source: Lucy Cohen

Burning Bush used for landscaping by a generator 

Image Source: Lucy Cohen

Winter Creeper photo taken during December

Image Source: Lucy Cohen taken at Powder Valley Nature Center in St. Louis

Honeysuckle used for landscaping in a backyard

Image Source: Lucy Cohen

Tree of Heaven during the Winter

Image Source: Lucy Cohen

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