Alternanthera philoxeroides

Alternanthera philoxeroides, commonly referred to as alligator weed, is a native species to the temperate regions of South America, which includes Argentina, Brazil, Paraguay and Uruguay. Argentina alone, hosts around 27 species that fall within the range of the genus Alternanthera. Its geographic range once used to cover only the Parana River region of South America, but it has since expanded to cover over 30 countries, such as the United States, New Zealand, China and many more. This invasive species is believed to have been accidentally introduced to these non-native regions through sediments trapped/attached to tanks and cargo of ships travelling from South America to these various areas. Alternanthera philoxeroides can thrive in both dry and aquatic environments and is characterized by whitish, papery flowers along its short stalks, irregular, or sprawling hollow stems, and simple and opposite leave pattern sprouting from its nodes. The species is dioecious. It is also considered a herbaceous plant due to its short-lived shoot system. It produces horizontal stems, otherwise known as stolons, that can sprout up to 10 m in length and thanks to its hollow stems, floats easily. This results in large clusters of stem to amass and create dense mats along the surface. The plant flowers from December to April and usually grows around 13 mm in diameter and tend to be papery and ball-shaped. The weed's intricate root system can either allow them to hang free in the water to absorb nutrients or directly penetrate the soil/sediment and pull their nutrients from below. Alternanthera philoxeroides is considered a major threat to ecosystems because of the adverse effects it poses on both aquatic and terrestrial environments, as well as negatively influence both the ecosystem and society. 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. As mentioned, the compact mats formed by this species can drive down the population of native vegetation in the environments it invades, this is a major issue for the native herbivore because their food source is declining. In addition, the dense mats present a challenge for the native wildlife by acting as a barrier between them and the natural water source. However, even if they can reach the water, they are still at risk because the water quality can be contaminated by the increased sediments. Thus, just as it did with the native vegetation, A. philoxeroides is also driving down the population of the native wildlife as well. 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. This invasive plant depends solely on vegetative means to reproduce and disperse itself in the area it has invaded and established its roots. In its native geographic range, the species spreads to through means of producing viable seeds; however, it has been observed within its non-native ranges that it rarely produces viable seeds. To accommodate this, the A. philoxeroides reproduces through fragmentation; the plant can regenerate itself from small portions of stems or small leaf cuttings. These small fragments of the plant can then be dispersed through human means and natural means; once its dispersed, the fragments can then find suitable ecological conditions and root itself and regenerate. In effort to eradicate the species by manual means, such as mulching or pulling them out, if not removed efficiently, small stem fragments can be displaced to new areas. Soil movement caused by earthmoving machinery is another example of how humans influence the dispersal of the plant.