Quick Facts

Quick facts

• Water Soldier (Stratiotes aloides) is a perennial waterplant with a large rosette of spiny, saw-edged leaves up to 50 cm long and with a long pointed tip.
• It looks similar to an Aloe (Aloe spp) or the top of a pineapple.
• It has foul smelling white flowers, but flowers and seeds are rarely produced and this species spreads mainly through vegetative growth.
• Plants float on the water surface in summer during flowering and sink to the bottom in autumn, where they over-winter as a rosette; in spring, the new leaves are buoyant and plants float to the surface.
• It is a vigorously growing plant that forms dense stands in suitable conditions.
• If introduced, it has the potential to become a serious aquatic weed of freshwater lakes, ponds, dams and wetlands in Australia.

What Does It Look Like?

What is it?

Water Soldier (Stratiotes aloides) is a perennial (long lived) aquatic herb that is usually floating and partly emergent in summer then submerged in winter. It has a rosette (basal cluster) of leaves and forms runners that develop new rosettes at their tips. Plants have a distinctive appearance: they resemble the top of a pineapple, or an aloe plant, but with showy white 3-petalled flowers. The rosette leaves are linear to very narrowly triangular or sword-shaped, pointed, triangular in cross-section, with numerous longitudinal parallel veins with cross-veins, and are brittle when handled. Submerged leaves are thin, soft, pale green to reddish and up to 60 cm long (although occasionally longer) and to 1 cm wide with little spines along the margins. Emergent leaves are thick, rigid, dark green, up to 40 cm long and 7–25 mm (but sometimes up to 40 mm) wide with well developed spines along the edges (they are more conspicuously sawtooth edged or serrated than the submerged leaves) (Stodola 1967; Mühlberg 1982; Cook & Urmi-König 1983; Spencer-Jones & Wade 1986; Sainty & Jacobs 2003; Jordan 2007; Johnson undated) .

There are separate male and female plants. At the top of a thick flower stalk up to 30 cm or more long, there is a two-leaved sheath that encloses one or rarely two flowers (in female plants), or three to six stalked flowers in male plants. These showy flowers have three white petals with a yellow patch in the centre, are up to 30 mm long (with female flowers smaller than male flowers) and foul-smelling (Stodola 1967; Mühlberg 1982; Cook & Urmi-König 1983; Spencer-Jones & Wade 1986; Sainty & Jacobs 2003; Jordan 2007; Johnson undated).

The fruit is a pulpy, flask-shaped, leathery, berry-like capsule, 12–34 mm long containing up to 24 cylindrical seeds. The roots either hang freely in the water or are anchored loosely in the mud. Plants may be entirely submerged, except when they rise to the water surface for flowering, or partly submerged with the leaf tips protruding out of the water (Stodola 1967; Mühlberg 1982; Cook & Urmi-König 1983; Spencer-Jones & Wade 1986; Sainty & Jacobs 2003; Jordan 2007; Johnson undated).

For further information and assistance with identification of Water Soldier, contact the herbarium in your state or territory.

Flower colour

White

Growth form (weed type/habit)

Aquatic, Herb

Where it currently grows? Preferred habitat

Water Soldier occurs in temperate areas, in still to slow-moving water, in shallow standing water, sheltered backwaters, pools, ponds, sluggish streams, drainage channels, ditches and canals, usually in nutrient-rich, loose, muddy substrates. It is sometimes found in sheltered bays or inlets of large lakes (Stodola 1967; Cook & Urmi-König 1983; Spencer-Jones & Wade 1986; Sainty & Jacobs 2003; Johnson undated). It can persist as a totally submerged plant in water 2–5 m deep, but is not found in temporary water or waterbodies that have great fluctuations in level (Cook & Urmi-König 1983).

Are there similar species?

Water Soldier is a very distinctive plant that is unlikely to be confused with other aquatic species.

Why Is It A Weed?

What are its impacts?

Native ecosystems: Overseas, Water Soldier has been introduced to new areas as an ornamental plant. It has a long history of being planted in moats, ponds and canals from where it has escaped to nearby natural waters (Cook & Urmi-König 1983), becoming a serious aquatic weed. It is a vigorous-growing plant that forms dense stands in suitable conditions making areas inaccessible. These dense stands can exclude native wetland plants and alter or destroy the habitat of fauna as well as choking waterways/waterbodies and interfering with waterflows, dams, navigation and recreational activities (Cook & Urmi-König 1983).

In Australia, Water Soldier has been declared in several states and features in weed and pest alerts because it has the potential to become a serious pest if it escapes from aquaria or outdoor ponds (Jordan 2007; Johnson undated). If introduced into the Australia environment, it has the potential to become a serious weed of freshwater lakes, ponds and dams (Jordan 2007; Johnson undated).

Water Soldier is a very strong competitor for nutrients and it also has an allelopathic effect, i.e., it produces chemical compounds that are released into the environment and these inhibit phytoplankton (Mulderij et al. 2005, 2006).

How does it spread?

Water Soldier reproduces vegetatively by shoots, as well as by hibernating winter buds produced in autumn. Water Soldier mostly spreads by vegetative reproduction in summer when lateral shoots are produced from the base of the plant and these break away to form new rosettes. Developing rosettes, sometimes still only bud like in formation, can be transported by water to new areas. New rosettes can also develop almost to maturity at the ends of the runners and later detach to take root or be transported by currents. Up to ten rosettes can form in a circle, filling the water surface and preventing other plants from growing (Cook & Urmi-König 1983; Johnson undated).

It can also reproduce by seed, but does not do so throughout most of its range (Cook & Urmi-König 1983; Stodola 1967; Johnson, undated). Male and female plants need to be growing in close proximity for sexual reproduction to occur. Seeds are dispersed by water and are released to float downstream when the seed capsule and plant becomes submerged at the end of summer (Johnson undated), or sink to the bottom as they are liberated from the fruit as a gelatinous mass (Cook & Urmi-König 1983).

What is its history in Australia?

Water Soldier is the only living species in the genus Stratiotes, but fossil records going back millions of years show the genus once included 15 other species that became extinct (Cook & Urmi-König 1983). .

How To Manage It?

Best practice management

Non-chemical control: Prevention: The best control is to prevent the introduction of Water Soldier into Australia. It should not be planted in aquaria or outdoor ponds. This is assisted by legislative control that declares its 'importation, possession and sale are prohibited' or warns 'do not introduce, keep or supply' this weed, and advises that, if found, plants 'should' or 'must be eradicated and prevented from spread' and 'land must be kept free of the plant'. As notifiable weeds in New South Wales and Queensland, all outbreaks must be reported to the appropriate state department. In New South Wales outbreaks can be reported to the New South Wales Department of Primary Industries and in Queensland they can be reported to the Department of Primary Industries and Fisheries (Jordan 2007; Johnson undated).

For contact information see http://www.dpi.nsw.gov.au/__data/assets/pdf_file/0006/144978/water-soldier-weed-alert.pdf  and http://www.dpi.qld.gov.au/cps/rde/xchg/dpi/hs.xsl/4790_7388_ENA_HTML.htm 

Overseas control has been difficult and is usually via mechanical means (Sainty & Jacobs 2003).

Does it have a biological control agent?

NO

When does it grow? (lifecycle/growth calendar)

Water Soldier has an interesting life cycle as it is usually a submerged plant but rises to the surface in spring to then flower in summer. New leaves that grow in spring contain air pockets which enable the plant to float. During summer the plants float just under the surface of the water with the upper parts of their leaves emerging above the surface. As the older leaves die back in autumn they become waterlogged, which causes the plant to sink again to the bottom where it stays during the winter as a rosette. During summer, there is vegetative reproduction as lateral shoots are developed from plant bases which bear terminal rosettes. These rosettes then produce new rosettes while attached to the parent plant or break away as 'buds' to form new rosettes. However, plants may remain submerged all year round (without flowering) in clear water 2–5 m deep (Mühlberg 1982; Cook & Urmi-König 1983; Sainty & Jacobs 2003; Johnson undated).

Flowering and fruiting takes place in a limited climatic range (Sainty & Jacobs 2003). For sexual reproduction and seed production to occur, male and female plants need to be growing in close proximity to one another. Each rosette forms a single flower stem generally in summer, though flowers may be produced from early spring onwards. Fruits are developed by early autumn, about the same time as some mature plants begin to sink. The fruit becomes submerged in late summer and autumn as the plants sink, releasing the seeds in a gelatinous mass, which sinks to the bottom. (Cook & Urmi-König 1983; Sainty & Jacobs 2003; Johnson undated).

Where Is It Found?

Which states and territories is it found?

Not found in any Australian states or territories.

What areas within states and territories is it found?

Water Soldier is not currently found in Australia.

Where does it originate?

Water Soldier is native to Europe (where it is becoming rare in some areas) and possibly part of Central Asia (Cook & Urmi-König 1983; GRIN 2008).

National And State Weed Listings

Is it a Weed of National Significance (WONS)?

NO

Where is it a declared weed?

NSW, QLD, SA

Government weed strategies and lists – Weeds Australia

Is it on the National Alert List for Environmental Weeds?

NO

Government weed strategies and lists – Weeds Australia

Is it on the Agricultural Sleeper List?

NO

Government weed strategies and lists – Weeds Australia

Names And Taxonomy

Main scientific name

Stratiotes aloides

Other scientific names (synonyms)?

Does it have other known common name(s)?

Water Soldiers, Crabs Claw, Water Aloe