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Alligator weed

Alternanthera philoxeroides

Description 11

Alligator weed, Alternanthera philoxeroides, is a non-woody perennial aquatic/shoreline plant found in Florida but non-native to the U.S.Leaves and stems vary greatly in size and shape. Fleshy, succulent stems can grow horizontally and float on the surface of the water, forming rafts, or form matted clumps which grow onto banks. The horizontal stems (called stolons) may reach a length of 10 m. The leaves are opposite in pairs or whorls, with a distinctive midrib, and range in size from 5-10 cm (Environment Waikato undated, Virginia Cooperative Extension undated).Fibrous roots arising at the stem nodes may hang free in water or penetrate into the sediment/soil. Flowers, which appear from December to April, are thin and clover-like in shape. The white flowers grow on stalks and are approximately 1.25-7.6 cm in length and 13 mm in diameter (Virginia Cooperative Extension undated).Alligatorweed occurs in a range of habitats ranging from dry terrestrial to aquatic. To facilitate buoyancy, plants growing in aquatic habitats tend to have stems that are hollow and larger than those of plants growing on land (Julien et al. 1992).

Impacts on society 12

Dense mats formed by this species influence the natural flow of water, which can impede various recreational activities, such as boating and fishing. The disruption of flow can also have a negative impact on infrastructure when it comes to energy, such as the use of hydro-electric dams to power generators. The dense mats also present suitable ecological conditions that mosquitoes can thrive off. This can be considered a commensal relationship between mosquitoes and A. philoxeroides because mosquitoes receive a breeding ground and the plant gets nothing nor losing anything. The increases population of mosquitoes can lead to increase risks towards humans’ health, regarding the spread of disease. Furthermore, the dense mats produced by A. philoxeroides do not present suitable ecological conditions for native species or humans to thrive off.

Impacts on vegetation 12

The presence of this invasive species disrupts the natural flow of water due to the dense mats created from its clusters of stems. It out competes the native vegetation for space and solar energy through these dense mats because they are large cluster and limit the amount of light that submerged vegetation receives. These compact clusters of stems also disturb the regular exchange of gases that occur underneath the surface that directly influences aerobic processes, such as photosynthesis. Aside from driving down the population of native aquatic vegetation, A. philoxeroides can also influence the growth and yield of crops in pastures and fields. These dense mats can affect the natural flow of water that is used in irrigation systems and as well as affect the quality of the water by increasing the sedimentation present in the water. Both factors are things that crops depend upon to not be disturbed, to provide a healthy yield for farmers, which is also falls within an impact it has on society that will be discussed later. On top of this, the likelihood of flooding is more like due to the drainage brought upon by the dense mats, which in turn can also damage the crops. Furthermore, this is a small insight into the negative impacts this invasive species has on the environment.

Preventive measures 12

Early detection is the best bet to ensure that the invasive species does not successfully colonize a non-native region because of its persistent to regenerate and propagate from small portions of its stem or leaf cuttings. However, when that is not possible, the best that can be done is to limit and control the presence of A. philoxeroides in an area. Alternanthera philoxeroides can only establish itself in shallow waters no deeper than 2 meters, so one method of control is to erect barriers in shallower areas to limit the amount of suitable space the plant has. When it comes to terrestrial environments, by overpopulating the area with native species it can limit the suitable space available for it. However, this method is only effective before the invasive plant has asserted itself in an area. Lastly, as previously mentioned, this plant is only able to produce viable seeds in its native geographic range and not in the areas it has invaded. By getting a better understanding on what ecological conditions make it so that only sterile seeds are produced in non-native regions could be key to developing further preventative measures against it.

Methods of control 12

Early detection is the best bet to ensure that the invasive species does not successfully colonize a non-native region because of its persistent to regenerate and propagate from small portions of its stem or leaf cuttings. However, when that is not possible, the best that can be done is to limit and control the presence of A. philoxeroides in an area. Alternanthera philoxeroides can only establish itself in shallow waters no deeper than 2 meters, so one method of control is to erect barriers in shallower areas to limit the amount of suitable space the plant has. When it comes to terrestrial environments, by overpopulating the area with native species it can limit the suitable space available for it. However, this method is only effective before the invasive plant has asserted itself in an area. Lastly, as previously mentioned, this plant is only able to produce viable seeds in its native geographic range and not in the areas it has invaded. By getting a better understanding on what ecological conditions make it so that only sterile seeds are produced in non-native regions could be key to developing further preventative measures against it.

Insects have been released for the biological control of A. philoxeroides. The most successful and widely used is Agasicles hygrophila commonly called the alligator weed flea beetle; it has been released for biocontrol in Australia, China, Thailand, New Zealand, and the United States. However, their effectiveness is limited due to their inability to survive through temperatures lower than 11 °C (52 °F). Amynothrips andersoni, the alligator weed thrips, and Vogtia malloi, the alligator weed stem borer, have also been released in the United States. These species result in immediate wilting and limit A. philoxeroides reproduction by colonizing its stems. A variety of chemicals have been shown to be effective in controlling the plant, the most useful of which include glyphosate, triclopyr, fluridone, imazamox, and imazapyr; however, they must be constantly be applied to be successful. Furthermore, these are all the currently known methods for control against the species.

Miscellaneous details 13

"Notes: Aquatic, Naturalized, Native of Tropical America"

Sources and Credits

  1. (c) eyeweed, some rights reserved (CC BY-NC-ND), http://www.flickr.com/photos/12626159@N05/3861901414
  2. (c) anonymous, some rights reserved (CC BY-NC-SA), https://collections.nmnh.si.edu/services/media.php?env=botany&irn=10287045
  3. (c) Jordan Broadhead, some rights reserved (CC BY-NC), uploaded by Jordan Broadhead
  4. (c) Alison Northup, some rights reserved (CC BY), uploaded by Alison Northup
  5. (c) Sam Kieschnick, some rights reserved (CC BY), uploaded by Sam Kieschnick
  6. (c) Andy Newman, some rights reserved (CC BY-NC), uploaded by Andy Newman
  7. (c) "<a href=""http://www.pwrc.usgs.gov/WLI/"">USDA NRCS Wetland Science Institute</a>.", some rights reserved (CC BY-NC-SA), https://plants.usda.gov/gallery/large/alph_001_lhp.jpg
  8. (c) "<a href=""http://www.wli.nrcs.usda.gov"">NRCS National Wetland Team, Fort Worth, TX</a>.", some rights reserved (CC BY-NC-SA), https://plants.usda.gov/gallery/large/alph_003_lvd.jpg
  9. (c) Jed Aplaca, some rights reserved (CC BY-NC), uploaded by Jed Aplaca
  10. (c) Brent Franklin, some rights reserved (CC BY-NC), uploaded by Brent Franklin
  11. (c) Smithsonian Marine Station at Fort Pierce, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/11525526
  12. (c) Wikipedia, some rights reserved (CC BY-SA), http://en.wikipedia.org/wiki/Alternanthera_philoxeroides
  13. (c) India Biodiversity Portal, some rights reserved (CC BY), http://eol.org/data_objects/26332690

More Info

Range Map

(c) Discover Life and original sources, some rights reserved (CC-BY-NC-SA)

iNat Map

Flower color white
Special status Federal noxious weed
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