Water soldier (Stratiotes aloides)

Synonyms: Stratiotes aloides L.

Common Names: Water soldiers, water aloe, water pineapple, crab's claw

Description:

Water soldier (Stratiotes aloides) is an invasive water plant from Europe and northwest Asia that looks like the floating top of a pineapple or an aloe plant [1][2]. It was sold for water gardens and has escaped into ponds, lakes, and slow rivers, where it forms dense beds of stiff, saw-toothed leaves [2][3]. MISIN tracks it because it is not yet established in our area, it crowds out native water plants, and its sharp-edged leaves can cut swimmers and snag boats [1][2].

Habit:

Water soldier grows as a rosette ? a tuft of stiff, sword-shaped bright green leaves spreading from a center, up to about 16 inches (40 cm) long [2]. The leaf edges are sharply saw-toothed, so the whole plant looks much like an aloe, a spider plant, or the leafy top of a pineapple sitting in the water [2]. It has an unusual yearly habit: in summer the rosettes float at the surface with the leaves sticking up, and in fall the plant gets coated with a slimy, lime-like layer and sinks to the bottom, rising again the next spring [2].

The easiest time to spot it is summer, when the rosettes float at the surface and may bear small white flowers [2]. The stiff, saw-toothed, sword-shaped leaves in a floating rosette are the giveaway [2].

At-a-glance cues:

1. Floating rosette of stiff, sword-shaped leaves up to about 16 inches long, like an aloe or pineapple top [2]
2. Leaf edges are sharply saw-toothed (serrated) and can cut skin [2]
3. Small white flowers with three petals in summer [2]
4. Floats at the surface in summer, then sinks to the bottom in fall [2]

Leaves:

1. Borne in a dense rosette ? a tuft radiating from the center of the plant [2]
2. Sword-shaped (long and tapering), stiff and brittle, bright green, up to about 16 inches (40 cm) long [2]
3. Edges are sharply serrated (saw-toothed) ? a key identifying feature and a cutting hazard [2]
4. Thick and somewhat keeled, broadest near the base [2]

Stems:

1. Largely stemless: the leaves form a basal rosette rather than rising on an upright stem [2]
2. Spreads outward on runners (stolons) that bear new daughter plants (offsets) [1][2]
3. Roots may dangle free or loosely anchor in the bottom; plants are often free-floating [2]
4. No woody parts [2]

Flowers:

1. Small and white, with three petals [2]
2. Held singly on a short stalk at the water surface in summer [2]
3. Male and female flowers grow on separate plants (dioecious) [1][3]
4. In North America only female plants are known, so flowering rarely leads to seeds [1][3]

Fruit and seeds:

1. Because only female plants occur in North America, fruit and seeds are rarely produced here [1][3]
2. Spread is almost entirely without seeds ? by daughter plants (offsets), tough overwintering buds (turions), and broken pieces that drift and root [1][2]
3. Any fragment of the plant can grow into a new one [2]

Habitat:

Water soldier lives in still or slow-moving fresh water ? ponds, lakes, slow rivers, canals, and wetlands ? and it favors calcium-rich (alkaline) water [1][2]. Plants float at the surface in the warmer months and rest on the bottom over winter [2].

The species is native to Europe and northwest Asia [1]. It was spread through the water-garden trade and has become established in Ontario, Canada; it is not established in the United States but is rated a high risk to spread here, including into the Great Lakes [1][3].

Reproduction:

Water soldier spreads mainly through people and moving water. It was sold as a water-garden plant, and it escapes or is dumped into natural waters [2]. Once it is present, it multiplies fast without seeds: each rosette sends out runners with new daughter plants, makes tough overwintering buds, and any broken piece can float away and grow into a whole new plant [1][2].

Because only female plants are known in North America, the plant almost never makes seeds here ? which means cutting or raking that breaks it up just creates more plants [1][3]. That is why the safest response is to avoid disturbing it, report it, and clean all gear before moving between waters so you do not carry fragments to a new site [2].

Impact and Damage:

For pond owners and people who use the water, water soldier forms dense beds that crowd a pond or shoreline and make boating, fishing, and swimming difficult [1][2]. Its sharply saw-toothed leaves can cut the skin of swimmers and waders, so it is a direct hazard as well as a nuisance [2]. The plant is not poisonous.

For natural areas, the dense floating rosettes shade out and displace native water plants, and thick beds can lower the light and oxygen in the water and change its chemistry, reducing habitat for fish and other wildlife [1][2]. Because it spreads so easily from fragments and is very hard to remove once established, an infestation is costly and long-lasting to manage [1].

Similar species:

Aloe (Aloe species) is the houseplant water soldier most resembles, with its rosette of serrated leaves ? but aloe leaves are thick and succulent, it grows in dry soil rather than water, and its flowers form a tall showy spike instead of single flowers [1].

Arrowheads (Sagittaria species) are native plants whose underwater rosettes can look similar, but their leaves are softer and not saw-toothed, and their three-petaled white flowers grow in groups rather than one at a time [1]. Sedges (Carex species) include some broad-leaved, clumping kinds that resemble water soldier, but their leaves are narrower, more flexible, and smooth-edged, and their flowers are not showy [1]. Bur-reeds (Sparganium species) have similar strap-like leaves, but the edges are not serrated and their flowers form round, ball-like heads along the stalk [1].

Monitoring and rapid response:

Signs to watch for:

1. Floating rosettes of stiff, saw-toothed, sword-shaped leaves ? an aloe or pineapple-top look ? on still or slow water in summer [2]
2. Small white three-petaled flowers at the surface in summer [2]
3. Plants that float in the warm months and sink to the bottom in fall [2]

What you can do:

1. Wear gloves ? the saw-toothed leaves can cut your skin [2].
2. Do not rake or pull large amounts: breaking the plant spreads it, because every fragment can grow into a new plant [1][2]. For a single stray plant, lift it out whole and carefully, keeping all the pieces.
3. Bag and dispose of any plants on land, away from the water; never compost or dump them, and never release water-garden plants into the wild [2].
4. Don't buy or plant water soldier ? choose native pond plants instead.
5. Clean, drain, and dry boats and gear before moving between waters [1].
6. Report it right away (below) ? early reports of this not-yet-established plant matter most [2].
7. Because fragments spread it, natural area crews and agencies control it with careful, contained hand-removal that captures every piece, sometimes with bottom barriers, repeated over several years ? as has been done in Ontario [1][2].

When to call a professional:

1. Any confirmed water soldier ? removing this fragment-spreading aquatic plant is a job for your aquatic invasive species or natural resources agency.
2. Established beds, or any plants in large or flowing water; check with your state aquatic agency before working in the water.
3. For chemical control options, contact a licensed applicator or your local cooperative extension office.

Report sightings to MISIN. Help track this species' spread by submitting observations through the MISIN web site or the MISIN mobile app (Android, iOS, Windows, and macOS). Photos at multiple angles paired with a precise GPS location are the most valuable data for confirming new occurrences and triggering rapid-response review.

Credits:

1. U.S. Fish & Wildlife Service. Ecological Risk Screening Summary: Water Soldiers (Stratiotes aloides) ? High Risk. fws.gov
2. Michigan Department of Natural Resources. Invasive Species: Water Soldier (Stratiotes aloides). michigan.gov/invasives
3. U.S. Geological Survey, Nonindigenous Aquatic Species Database. Stratiotes aloides ? Species Profile. nas.er.usgs.gov
4. Wisconsin Department of Natural Resources. Water Soldiers (Stratiotes aloides). dnr.wisconsin.gov

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