Apiospermun obcordatum (Schleid.) Klotzsch, Limnonesis commutate (Schleid.) Klotzsch, Limnonesis friedrichsthaliana Klotzsch, Pistia aegyptiaca Schleid, Pistia aethiopica Fenzl ex Klotszch, Pistia africana C. Presl, Pistia amazonica C. Presl, Pistia asiatica Lour., Pistia brasiliensis Klotszch, Pistia commutata Schleid, Pistia crispate Blume, Pistia cumingii Klotszch, Pistia gardneri Klotszch, Pistia horkeliana Miq., Pistia leprieuri Blume, Pistia linguiformis Blume, Pistia minor Blume, Pistia natalensis Klotzsch, Pistia obcordata Schleid, Pistia occidentalis Blume, Pistia schleideniana Klotzsch, Pistia spathulata Michx., Pistia stratiotes var cuneata Engl., Pistia stratiotes var obcordata (Schleid.) Engl., Pistia stratiotes var spathulata (Michx.) Engl., Pistia texensis Klotzsch, Pistia turpini Blume, Pistia turpinii K. Koch, Pistia weigeltiana C. Presl, floating aroid, Nile cabbage, pistia, shell-flower, tropical duckweed, water bonnet, water cabbage, water fern, water lily, laitue d'eau, pistie, Lechuguilla de agua, lechuguita de agua, repollo de agua (Global Invasive Species Database 2005, CABI 2014)

• Leaves: gray-green, about 10-20 cm long, widest at the apex, spongy near the base, with dense white hairs, 7-15 prominent parallel veins, and arranged in rosettes (i.e. circular leaf arrangement).
• Stolons (i.e. stem or runner): arise from leaf axis, up to 70 cm long, and entangle to create floating mats.
• Roots: covered with fine root hairs which give them a feather-like appearance, dense, and hang unbranched about 50 cm below the water.
• Flowers: inconspicuous and clustered on small, fleshy stalks that are nearly hidden in the leaf axils. Flowers are single sexed with male: 3-9 flowers whorled above a single female flower.
• Fruit: green berry with many seeds.

FOOD WEB: This species is an autotroph.

LIFE HISTORY: Pistia stratiotes reproduces asexually and sexually. It can spread rapidly by vegetative fragmentation from offshoots on short, brittle stolons. Also, seed production is now considered a major method of reproduction and dispersal (Dray and Center 1989). P. stratiotes possess both male and female flowers. Seeds are wind and insect pollinated and mature 30 days after fertilization (Parsons and Cuthbertson 2001). Seeds can disperse by water and sink into the mud or stream bed, and germinate in light at temperatures above 20 °C. Seedlings float to the surface once the primary leaf has developed. Each plant produces several stolons that are about 60 cm long that terminate in rosettes and can become fragmented to produce new plants.

Pistia stratiotes is frequently reported in shallow waters of the Great Lakes basin. During spring through the fall, P. stratiotes is found in Lake St. Clair (Adebayo et al. 2011), Detroit River, and inland waters (Cochran et al. 2006). These populations are not believed to be self-sustaining but rather to stem from frequent re-introductions.

This species is common in the aquarium trade (Parsons and Cuthbertson 2001). According to a study on aquarium and pet stores near Lakes Erie and Ontario, 20% of stores surveyed carried Pistia stratiotes (Rixon et al. 2005). P. stratiotes may be released into the Great Lakes when aquarists dispose of this plant into waterways. This species is also planted in water gardens and may be unintentionally introduced to the Great Lakes. P. stratiotes spreads via vegetative fragmentation and water dispersal of seeds. Fragments or seeds of P. stratiotes may potentially be introduced to the Great Lakes by dispersal from cultured populations. P. stratiotes can also be unintentionally transported to the Great Lakes by hitchhiking on boats and recreational equipment between bodies of freshwater.

Predicted increase in winter water temperatures in the Great Lakes region due to climate change may increase the probability of this species becoming self-sustaining as an annual (Adebayo et al. 2011).

Pistia stratiotes has a moderate probability of establishment if introduced to the Great Lakes (Confidence level: High).

The recurrence of Pistia stratiotes on the southern shores of Lake St. Clair for three consecutive years raised suspicion that the macrophyte may have been overwintering in the basin. However, MacIsaac et al. (2016) did not find evidence of seed production—indicating that the persistence of P. stratiotes in the Great Lakes is likely dependent upon annual reintroduction by humans. P. stratiotes reproduces rapidly through seed production and vegetative fragmentation. Its short, brittle stolons that are involved in vegetative fragmentation allow populations to expand rapidly and may aid its establishment in the Great Lakes.

P.stratiotes does best in warm waters, as it is killed by frost. P. stratiotes exhibits optimal growth at water temperatures of 22-30 °C (Kasselmann 1995). Plants can tolerate temperatures as low as 15 °C and as high as 35 °C (Rivers 2002). This species has been observed to overwinter in the Erft River, Germany; the water temperature in that river is abnormally warm (>11 °C) and only leaves that remained submerged survived (Hussner et al. 2014). Its seeds can survive for at least 2 months in water at 4°C and for a few weeks in ice at -5 °C (Parsons and Cuthbertson 2001), and so the seeds of P. stratiotes have the potential to overwinter in the Great Lakes. However seeds require temperatures above 20°C to germinate, which results in a growing season too short for these individuals to set seed themselves. Locations where water temperatures warm earlier than typical for the region or where frost is significantly delayed, such as thermal outfalls, may allow local populations to overwinter, though we currently find no direct evidence that this has occurred.

The native and introduced ranges of Pistia stratiotes have somewhat similar climatic and abiotic conditions as the Great Lakes; except the Great Lakes has lower air temperatures and lower water temperatures. The effects of climate change may make the Great Lakes a more suitable environment for the establishment of P. stratiotes. Warmer water temperatures and shorter duration of ice cover would aid the establishment of P. stratiotes. Shallow lakes and slow-flowing streams in the Great Lakes may provide suitable habitats for P. stratiotes with even modest warming.

Pistia stratiotes has outcompeted other species where it has been introduced. Three years after P. stratiotes was first observed in Slovenia, it had covered the whole water surface and populations of native freshwater plants, Ceratophyllum demersum, Myriophyllum spicatum, Najas marina, and Trapa natans, had declined (Šajna et al. 2007).

Surveillance and management efforts are currently underway to detect, control, and/or eradicate this plant in Michigan (MI DEQ 2013) and Wisconsin (Falk et al. 2010) which may help to prevent establishment.

Summary of species impacts derived from literature review. Click on an icon to find out more...

Environmental	Socioeconomic	Beneficial

Pistia stratiotes can have detrimental effects on the environment and other species due to its production of allelochemicals, which inhibits algae growth (Aliotta et al., 1991). Additionally, it causes high evapotranspiration rates (Sharma, 1984) and forms dense mats that reduce light availability for submerged macrophytes and planktonic algae (Attionu, 1976). These factors, along with its impact on water temperature, pH, stratification, and oxygen levels, can lead to adverse consequences for native plants, fish, and wildlife (Attionu, 1976; Šajna et al., 2007; Sridhar and Sharma, 1986, FL DEP 2007). In Slovenia, the presence of P. stratiotes resulted in a decline in native freshwater plants three years after its introduction (Šajna et al., 2007).

Pistia stratiotes has the potential for high socio-economic impact if introduced to the Great Lakes.

Pistia stratiotes is among the world’s worst weeds (Holm 1991) and has received significant media attention (e.g. de la Cruz 2014, Spear 2014).

Pistia stratiotes mats provide habitat for disease carrying mosquitos, such as malaria vectors Anopheles and Mansonia (FL DEP 2007, Lounibos and Dewald 1989, Parsons and Cuthbertson 2001, Rejmankova et al. 1991). Mansonia larvae perforate leaves and roots of P. stratiotes to reach air chambers (Lounibos and Dewald 1989). Taeniorhynchus (Mansonioides) africanus and Anopheles gambiae breed in ponds and streams that are clogged with P. stratiotes (Philip 1930).

Pistia stratiotes causes damages to infrastructure. Infestations of this species can block waterways, reducing the efficiency of irrigation and hydroelectric power (Howard and Harley 1998). Dense mats of P. straiotes reduce water flow, damages flood control structures, and can create dams against bridges (FL DEP 2007). Pistia stratiotes may impact recreation, as it interferes with navigation and fishing (Labrada and Fornasari 2002). Florida spent about $1.4 million dollars in 2005-2006 to treat P. stratiotes (FL DEP 2007).

Pistia stratiotes has the potential for moderate beneficial impact if introduced to the Great Lakes.

Pistia stratiotes is also used in traditional medicine for its therapeutic properties (Tripathi et al. 2010, Saddam et al. 2018, Abubakar et al. 2020). Research has been conducted to utilize this species for biofuels (Lu et al. 2010, Mishima et al. 2008). Pistia stratiotes is among one of the most common macrophyte species sold in aquarium stores around Lake Ontario and Erie (Rixon et al. 2005).

Pistia stratiotes is a potential candidate for the removal of heavy metals from contaminated water (Odjegba and Fasidi 2004, Ali et al. 2020, Leblebici et al. 2019, Vieira et al. 2019). Numerous experiments P. stratiotes could be used to remediate runoff from a variety of sources including nursery, greenhouse operations, domestic sewage, textile factories, rice mills, paper mills, and sugar mills  (Sridhar and Sharma 1980, Polomski et al. 2009,  Kumar et al. 2018, Ferreira et al. 2019, Schwantes et al. 2019, Kumar et al. 2020,Ekanayake et al. 2021). Several experimental trials indicate that P. stratiotes can dissipate herbicides, and so this plant could decontaminate waters near agricultural areas (Barchanska et al. 2019, Escoto et al. 2019, Alencar et al. 2020, Alonso et al. 2021).

*Table last updated 7/05/2022. Always check federal, state/provincial, tribal and local regulations directly for the most up-to-date information.

Surveillance and management efforts are currently underway to detect, control, and/or eradicate this plant in Michigan (MI DEQ 2013) and Wisconsin (Falk et al. 2010).

Control

Biological

Biological control techniques such as the utilization of specialist herbivores (e.g. Spodoptera pectinicornis, Neohydronomus affinis) have shown to reduce P. stratiotes infestations in several cases (Cilliers 1991; Wheeler et al. 1998; Harley et al. 1990; Diop and Hill 2009). In Australia, Neohydronomus affinis reduced P. stratiotes populations by 40% or more within 12-18 months (Harley et al. 1990). However, N. affinis has been reported to have limited impact in seasonally flooded areas infested with Pistia stratiotes (Cilliers et al. 1991).

Additionally, it is possible that Microcystis blooms in the Great Lakes may impact P. stratiotes populations if the species became established in the basin. Microcystin-LR is the predominant toxin produced by Microcystis in the lower Great Lakes (Dyble et al. 2009). P. stratiotes is capable of removing the cyanobacterial hepatotoxin [Dha⁷] microcystin-LR (MC-LR) by bioaccumulating the toxin in its roots and leaves. However, exposure to the toxin at concentrations of 0.5 and 1.0 mg/L resulted in a decreased root length by 9.15% and 18.59%, respectively. In addition to shortened and rotting roots, the leaves of P. stratiotes turned yellow and rotted off (Somdee et al. 2016).

Physical

In Botswana, research has shown that manipulation of water levels paired with physical removal of P. stratiotes at regular intervals prior to anthesis reduced seed germination in surface sediment samples from 63.5%  to 31.7% in a one year span (Kurugundla 2014). Additionally, mechanical harvesters and chopping machines can help remove water lettuce from the water by grinding the plant down to bits (Ramey 2001).

Chemical

In general, the most common herbicides used to control floating aquatic weeds are 2,4-D, Diquat, and Glyphosphate (Howard and Harley 1998). Herbicides may cause weed die-off and subsequent decomposition that may remove dissolved oxygen from the water. Herbicides might not be able to kill the seeds of the floating aquatic weed.

Note: Check state/provincial and local regulations for the most up-to-date information regarding permits for control methods. Follow all label instructions.