Species Profile - Water soldiers

Stratiotes aloides L.

Common Name: Water soldiers

Synonyms and Other Names:

Water Pineapple, Saw Tooth, Water Aloe

Identification: Water Soldiers, Stratiotes aloides (Family: Hydrocharitaceae), is a loosely rooted aquatic species with emergent and submerged growth forms (Cook and Urmi-König 1983; Erixon 1979). S. aloides has depressed conical stems with a complex but regular branching system that can resemble the household spider plant (Campbell 2009) . Water soldiers' serrated leaf edges distinguish it from similar looking aquatic plants in the Great Lakes (MNRF 2014). Submerged leaves are thin, brittle and droop at an angle. Submerged leaves can grow up to 60 cm (or rarely 110 cm long) and up to 1 cm wide with somewhat weak spines. Emergent leaves are thick, rigid, brittle, and dark green and are usually less than 40 cm long and 1-4 cm wide, with well-developed spines along leaf margins. The emergent form develops rosettes at the surface of the water (Cook and Urmi-König 1983). The roots of S. aloides can be up to 180 cm long but are usually less.

Size: Stem length: 10-18mm long, Leaf length: 40-60 cm long, 1-4 cm wide (Cook and Urmi-König 1983).

Native Range: Stratiotes aloides is native from the United Kingdom through to Asia. Specifically, the United Kingdom, Spain, Italy, Bulgaria, and Siberia (UK Natural History Museum 2013).

Nonindigenous Occurrences: The only wild populations of S. aloides in North America occur in five locations within the Trent River and Black River in Ontario, Canada: (1) In the Trent River approximately between the town of Trent River and the south end of Crowe Bay, but scattered plants have been found as far as the east end of Percy Reach, County of Northumberland; (2) in a watering pond for cattle in Trent Hills, County of Northumberland; (3) in a pond at Blackstock in the Township of Scugog, Regional municipality of Durham; (4) in an artificial pond near Bayfield, Huron County; and (5) in the Black River, near Sutton, Regional Municipality of York (Snyder et al. 2016).

This species is not currently in the Great Lakes region but may be elsewhere in the US. See the point map for details.

Table 1. States/provinces with nonindigenous occurrences, the earliest and latest observations in each state/province, and the tally and names of HUCs with observations†. Names and dates are hyperlinked to their relevant specimen records. The list of references for all nonindigenous occurrences of Stratiotes aloides are found here.

State/Province	First Observed	Last Observed	Total HUCs with observations†	HUCs with observations†
ONT	2016	2021	*

Table last updated 5/16/2022

† Populations may not be currently present.

* HUCs are not listed for areas where the observation(s) cannot be approximated to a HUC (e.g. state centroids or Canadian provinces).

Ecology: Stratiotes aloides usually inhabits shallow stagnant waters, mainly eutrophic and mesotrophic, with substratum of mud and organic deposits (Strzalek and Koperski 2009). Stratiotes aloides can grow in depths of up to 6.5m (Tarkowska-Kukuryk 2006). Stratiotes aloides is found mainly in sheltered bays of larger lakes, backwater ponds, ditches and canals (UK Natural History Museum 2013). Stratiotes aloides is limited to freshwater. Stratiotes aloides ranges as far north as Kittila, Finland (Kittila is located at 67°N), where the coldest temperatures in Finland occur.

This species has vegetative reproduction. Vegetative propagules are formed as axillary buds. When the bottom leaves of the rosette decay, these buds are released. On average 4.7 (±0.28 SE) buds are formed per mature rosette (n = 83) (Sarneel 2013). Buds have high capacity to disperse over long distances via water (84% of propagules re-sprouted, and 92% were still floating after 187 days) (Sarneel 2013).

Means of Introduction: Stratiotes aloides has a high probability of introduction to the Great Lakes (Confidence level: High).

Potential pathway(s) of introduction: Dispersal, Hitchhiking/Fouling, and Stocking/Planting/Escape from Recreational Culture

Stratiotes aloides occurs in the Trent River, Ontario, with a population of over 22,000 plants (Campbell 2009). Aquatic macrophytes are commonly found on trailered boats, and the Trent-Severn waterway is a popular destination for boaters (http://thewaterway.ca/#sthash.L82cPc3u.dpbs). The infestation in the Trent River began as an accidental escape (Ontario Ministry of Natural Resources 2009, 2014).

Status: The only invasive population reported has been in Ontario. What would have likely started from a few plants has grown to 22,000 plants in seven populations.

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

Stratiotes aloides has been described by government agencies as likely to crowd out native vegetation (Ontario Ministry of Natural Resources 2009, 2014), though no primary literature exists to support this in introduced habitats. It does form "dense, almost monospecific stands" in native habitat (Strzalek and Koperski 2009). Most species in the genus produce vegetative fragments and reproduce easily. Stratiotes aloides can overwinter in the Great Lakes; the population in Finland overwinters fine in temperatures similar to those experienced in the Great Lakes.

Great Lakes Impacts: Stratiotes aloides has the potential for moderate environmental impact if introduced to the Great Lakes.

Stratiotes aloides forms "dense, almost monospecific stands" in native habitat (Strzalek and Koperski 2009) and has the potential to crowd out native vegetation (Ontario Ministry of Natural Resources 2009).

Stratiotes aloides has the potential to alter surrounding water chemistry, which may harm phytoplankton and other aquatic organisms (Ontario Ministry of Natural Resources 2009). The exact mechanism has not been elucidated, but the likely cause is allelopathy (Mulderij et al. 2006).

Stratiotes aloides has the potential for moderate socio-economic impact if introduced to the Great Lakes.

Stratiotes aloides’s sharp leaves can cut skin (CommunityPress.ca 2009). Dense floating mats of Water Soldier can hinder recreational activities, such as boating, angling, and swimming. This would likely result from a massive infestation, but has not been quantified.

There is little or no evidence to support that Stratiotes aloides has the potential for significant beneficial impacts if introduced to the Great Lakes.

It has not been indicated that Stratiotes aloides can be used for the control of other organisms or improving water quality. There is no evidence to suggest that this species is commercially, recreationally, or medically valuable. It does not have significant positive ecological impacts.

Management:

Regulations

It is illegal to import, possess, deposit, release, transport, breed/grow, buy, sell, lease or trade S. aloides in Ontario (Invasive Species Act 2015). Michigan prohibits the introduction, importation, movement, sale, or distribution of S. aloides (NREPA Part 413 as amended, MCL 324.41302(3)(a)). Illinois lists S. aloides as an injurious species as defined by 50 CFR 16.11-15. Therefore, S. aloides cannot be possessed, propagated, bought, sold, bartered or offered to be bought, sold, bartered, transported, traded, transferred or loaned to any other person or institution unless a permit is first obtained from the Department of Natural Resources. Illinois also prohibits the release of any injurious species, including S. aloides (17 ILL. ADM. CODE, Chapter 1, Sec. 805). Wisconsin prohibits the transport, possession, or introduction of S. aloides (Wisconsin Chapter NR 40). It is also prohibited for a person to possess, import, purchase, sell, propagate, transport, or introduce S. aloides in Minnesota (Minnesota Rule 6216.0250). There are no regulations on S. aloides in New York, Pennsylvania, Ohio, Michigan, or Indiana.

Note: Check federal, state, and local regulations for the most up-to-date information.

Control

Biological

Herbivorous birds and fish may be able to limit the establishment and growth of S. aloides in the Great Lakes basin. Veen et al. (2013) found that grazing by a variety of vertebrate aquatic herbivores reduced the biomass growth of S. aloides by 60% and resulted in decreased survival over 16 weeks. S. aloides is also vulnerable to fungi such as Fusarium roseum (Cook and Urmi-Konig 1983), but use of any pathogenic control should be cautiously employed in order to minimize non-target effects.

Physical

Despite being less efficient, removal by hand in the Trent River, Ontario was found to be initially as effective as chemical treatments. However, difficulty in detecting S. aloides in dense macrophyte communities and turbid water reduce the efficacy of hand removal (Anonymous 2014 in Snyder et al. 2016). Shade-cloth enclosures designed to prevent sunlight were utilized on three populations of S. aloides in Ontario. After two months, all water soldiers plants covered by the enclosures were deceased (Ontario’s Invading Species Awareness Program 2016). Other physical control methods, such as mechanical harvesting, have not been conclusively evaluated (Snyder et al. 2016).

Chemical

Several studies investigating the efficacy of diquat revealed that at least 16 hours of 370 ug L-1 was required to achieve a complete collapse of plants without any regeneration over the following six weeks. However, the effectiveness of diquat is limited in deep, fast-flowing, or turbid water (Snyder et al. 2016). In order to minimize non-target impacts, herbicide treatments should be conducted in Fall (September and October) when water soldiers remain actively growing and other native aquatic plants have gone dormant (MNRF 2016).

Intensified agricultural practices and anthropomorphic stressors over the last half century have contributed to the decline of S. aloides in parts of Europe (Smolders et al. 2003; Abeli et al. 2014). Smolders et al. (2003) determined that the decline of S. aloides is mainly due to increased sulphate reduction rates, which can lead to sulphide toxicity, iron deficiencies, and increased internal eutrophication due to mobilization of phosphate. Additionally, increased competition from free-floating plants and increased ammonium concentrations also have contributed to its decline. Sites in Italy where S. aloides had been extirpated were characterized by high inorganic nitrogen concentrations and low CO2 concentrations (Abeli et al. 2014). Therefore, eutrophication events that are seen in areas like Green Bay and the Western Basin of Lake Erie may affect S. aloides if it were to become established in these areas.

Note: Check state and local regulations for the most up-to-date information regarding permits for pesticide/herbicide/piscicide/insecticide use.

References:

Abeli, T., G. Rossi, A.J.P. Smolders, and S. Orsenigo. 2014. Nitrogen pollution negatively affects Stratiotes aloides in Central Eastern Europe. Implications for translocation actions. Aquatic Conservation: Marine and Freshwater Ecosystems 24(5):724-729. dx.doi.org/10.1002/aqc.2497.

Campbell, J. 2009. Water soldier the newest recruit in army of invasive species. Community Press, Trenton, Ontario, Canada. 2009 (August 17). http://www.communitypress.ca/ArticleDisplay.aspx?e=1703308.

Cook, C.D.K., and K. Urmi-König. 1983. A revision of the genus Stratiotes (hydrocharitaceae). Aquatic Botany 16(3):213-249.

Erixon, G. 1979. Population ecology of a Stratiotes Aloides L. stand in a riverside lagoon in N. Sweden. Hydrobiologia 67(3):215-221. dx.doi.org/10.1007/BF00023178.

Mulderij, G., A.J.P. Smolders, and E. Van Donk. 2006. Allelopathic effect of the aquatic macrophyte, Stratiotes aloides, on natural phytoplankton. Freshwater Biology 51(3):554-561. dx.doi.org/10.1111/j.1365-2427.2006.01510.x.

Ontario's Invading Species Awareness Program. 2016. Outreach, surveillance and control of invasive water soldier. Ontario Wildlife Foundation.
Ontario Ministry of Natural Resources. 2009. Water Soldier (Stratiotes aloides). http://www.mnr.gov.on.ca/stdprodconsume/groups/lr/@mnr/@biodiversity/documents/document/stdprod_104417.pdf.

Ontario Ministry of Natural Resources and Forestry (MNRF). 2014. Water Soldier (Stratiotes aloides). https://dr6j45jk9xcmk.cloudfront.net/documents/3234/stdprod-104417.pdf. Created on 07/17/2014. Accessed on 04/24/2017.

Ontario Ministry of Natural Resources and Forestry (MNRF). 2016. First Public Notice: Proposed invasive species control measure in the Trent River. Ontario Ministry of Natural Resources and Forestry, Peterborough, Ontario.

Sarneel, J.M. 2013. The dispersal capacity of vegetative propagules of riparian fen species. Hydrobiologia 710(1):219-225. dx.doi.org/10.1007/s10750-012-1022-3.

Smolders, A.J.P., L.P.M. Lamers, C. den Hartog, and J.G.M. Roelofs. 2003. Mechanisms involved in the decline of Stratiotes aloides L. in the Netherlands: sulphate as a key variable. Hydrobiologia 506(1):603-610. dx.doi.org/10.1023/B:HYDR.0000008551.56661.8e.

Snyder, E., A. Francis, and S.J. Darbyshire. 2016. Biology of invasive alien plants in Canada. 13. Stratiotes aloides L. Canadian Journal of Plant Science 96:225-242. dx.doi.org/10.1139/cjps-2015-0188.

Strzalek, M., and P. Koperski. 2009. The Stratiotes aloides L. stand as a habitat in oxbow lake Buzysko. Aquatic Botany 90(1):1-6. dx.doi.org/10.1016/j.aquabot.2008.04.010.

Tarkowska-Kukuryk, M. 2006. Water soldier Stratiotes aloides L. (Hydrocharitaceae) as a substratum for macroinvertebrates in a shallow eutrophic lake. Polish Journal of Ecology 54(3):441-451. https://miiz.waw.pl/pliki/article/ar54_3_13.pdf.

UK Natural History Museum. 2013. Stratiotes aloides. http://www.nhm.ac.uk/our-science/data/uk-species/species/stratiotes_aloides.html. Accessed on 07/01/2015.

Veen, G.F., J.M. Sarneel, L. Ravensbergen, N. Huig, J. Van Paassen, W. Rip, and E.S. Bakker. 2013. Aquatic grazers reduce the establishment and growth of riparian plants along an environmental gradient. Freshwater Biology 58(9):1794-1803. dx.doi.org/10.1111/fwb.12168.

Other Resources:

United Kingdom Natural History Museum

Trent-Severn Waterway

Ontario's Invading Species Awareness Program

Author: Fusaro, A., A. Davidson, K. Alame, M. Gappy, E. Baker, G. Nunez, J. Larson, W. Conard, and P. Alsip

Contributing Agencies:

Revision Date: 5/11/2017

Citation for this information:
Fusaro, A., A. Davidson, K. Alame, M. Gappy, E. Baker, G. Nunez, J. Larson, W. Conard, and P. Alsip, 2022, Stratiotes aloides L.: U.S. Geological Survey, Nonindigenous Aquatic Species Database, Gainesville, FL, and NOAA Great Lakes Aquatic Nonindigenous Species Information System, Ann Arbor, MI, https://nas.er.usgs.gov/queries/greatLakes/FactSheet.aspx?Species_ID=3159&Potential=Y&Type=2&HUCNumber=DGreatLakes, Revision Date: 5/11/2017, Access Date: 5/17/2022

This information is preliminary or provisional and is subject to revision. It is being provided to meet the need for timely best science. The information has not received final approval by the U.S. Geological Survey (USGS) and is provided on the condition that neither the USGS nor the U.S. Government shall be held liable for any damages resulting from the authorized or unauthorized use of the information.