Weed Alert: Water soldier

Water Soldier (Stratiotes aloides)

World Status | Identification | Growth and Spread | | Control | Legislation

Water soldier is a plant that has the potential to become a serious aquatic weed of freshwater lakes, ponds and dams in Australia. It is a vigorous growing plant that forms dense stands in suitable conditions. These dense stands can exclude native wetland plants and destroy the habitat of fauna.

Because water soldier leaves resemble aloe plants it is also called water aloe.

World Status

Water soldier is a native of Europe and is not currently found in Australia.It has the potential to become a serious pest if it escapes from aquariums or outdoor ponds.

Identification

Water soldier plants have a distinct appearance in that they resemble the top of a pineapple.

Leaves

Leaves extend from a rosette, are long and narrow with a slightly triangular shape.Submerged leaves are light green and up to 60 cm long with little spines along the margins. Emergent leaves are a dark green, less than 40 cm long and 1–4 cm wide with well developed spines along the margins. The leaves are very brittle.

Flowers

Very little in known about the conditions required for flowering in this species. The flower-stalk is short and thick, about 15 cm high. At the top of the stalk is a two-leavedsheath, like the claws of a crab. The sheath contains several delicate white flowers, with three petals and numerous stamens. The flower develops into into a pulpy, flask shaped berry.

Roots

Roots either hang free in the water or more usually are loosely rooted in the mud.

Growth and Spread

Water soldier has an unusual growth habit. It is a submerged plant except in summer when it rises to the water surface to flower. The new leaves that grow in spring contain air pockets which allows the plant to float. As the older leaves die back in autumn they become waterlogged which causes the plant to sink again. Water soldier can remain submerged all year round and can grow in depths of up to five metres.

Water soldier can reproduce vegetatively and by seed. It mostly spreads by vegetative reproduction in summer when lateral shoots are produced from the base of the plant which break away to form new rosettes. Up to eight or ten rosettes can form in a circle, filling the water surface and preventing all other plants from growing.

To reproduce by seed, male and female plants need to be growing in close proximity. Each rosette forms a single flower stem in summer. The seed capsule becomes submerged at the end of summer as the plants sink, allowing seeds to float downstream.

Control

For control advice contact your Council Weeds Officer or NSW Department of Primary Industries

Legislation

Stratiotes aloides is a Class 1 noxious weed throughout NSW under the Noxious Weeds Act 1993. This weed must be eradicated from the land and the land must be kept free of the plant. As a notifiable weed, all outbreaks must be reported to the local control authority within three days.

Acknowledgements

Prepared by Annie Johnson.

References

• Cook, C.D.K. and Urmi-Konig, K. (1983) A revision of the genus Stratiotes (Hydrocharitaceae) Aquatic Botany. 16:213–249.