Alligatorweed (Alternanthera philoxeroides)


There’s no armored body, sharp teeth or long round snout on the Alligatorweed, but this invasive plant, however, is known for the damage it can cause.

Alligatorweed, or Alternanthera philoxeroides, forms thick mats that crowd out native aquatic vegetation, reduce water flow, lower dissolved oxygen levels, and increase sedimentation. The plant can cause flooding by impeding drainage and restrict water flow for irrigation. It can also hurt fishing opportunities and other water recreation.

This invasive plant is one among other invasive water plants in Texas, including hydrilla, water hyacinth and water lettuce. Invasives thrive when introduced into areas where they have no predators or disease control. They quickly reproduce and grow unchecked, crowding out native species that use the same habitat.

Native to South America, the Alligatorweed was introduced into the U.S. around 1900, according to texasinvasives.org. This invasive lives in shallow water or wet soils, ditches, marshes, edges of ponds and slow-moving watercourses and can tolerate cold winters and warm summers.

Unlike other invasives that are easy to identify, identification of alligatorweed often requires a trained eye as it has two native lookalikes, water willow and water smartweed.

Its stems are hollow and white; sweet-scented flowers bloom amongst the oval-shaped leaves. Once established, Alligatorweed spreads rapidly and is difficult to remove, according to the Texas Invasive Species Institute. Physical removal of the invasive isn’t 100 percent successful because it can re-grow from stem fragments alone. There are currently no biological control methods of eradication rather than goats, which feed on the weed, according to the Texas Invasive Species Institute.

The BRA works to prevent the spread of invasive species by supporting Texas Parks and Wildlife’s public outreach campaign. The BRA also performs routine observations by environmental services staff that identify exact species, assess threats to reservoirs, and treat if needed.

The biggest threat to our ecosystem when invasive species are introduced would be the reduction of natural biodiversity, reduced food source for native wildlife, and low dissolved oxygen problems.

Prevention is key to stop the spread of invasive plants such as hyacinth, hydrilla, alligatorweed and water lettuce. If you visit waterbodies known to have invasive plants, please follow TPWD’s recommendations to clean, drain and dry your boat, canoe, or kayak before visiting other waterbodies.

As a non-native plant, it is illegal to possess or transport Alligatorweed in Texas. Report sightings to the Texas Parks and Wildlife Department at (512) 389-4800. If you believe you have observed Alligatorweed on any BRA reservoir, please document the location along with a photograph, if at all possible, and report the sighting to the lake office.