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Pistia stratiotes L.
Family Araceae
Common name: Water Lettuce, Nile Cabbage

Pistia stratiotes L. APNI*

Description: Lettuce-like, stoloniferous, free-floating, mat-forming, perennial, aquatic herb with leaves in rosettes to c. 30 cm diam.; plants may also be attached to mud. Horizontal runners (stolons) up to 60 cm long produce new plants at their tips; rosette bases with trailing feathery roots to 1 m long hanging below water surface.

Leaves overlapping, ± spathulate to broad-ovate or fan-shaped, pale green, yellowish green or grey-green, 2–17 cm long, 1.5–8.5 cm wide, spongy, longitudinally ribbed, softly velvety hairy; petiole much shortened and inflated.

Inflorescence small, 7–20 mm long, amongst the leaf bases, whitish green. Pistil partly fused to spathe. Male zone a whorl of stamens terminating a short free part of the spadix above a flap of spathe tissue.

Berry ovoid to ellipsoid, 5–10 mm long, greenish.

Photo A.E. Orme

Flowering: throughout year.

Distribution and occurrence: Naturalised in coastal districts north from Sydney. Native of northern Australia (Northern Territory and possibly northern Queensland) and pantropropical regions. A declared noxious weed in this State.

Grows on open, still or slow-moving water, in lakes, ponds, streams, wetlands, farm dams and reservoirs.
NSW subdivisions: *NC, *CC
Other Australian states: *Qld N.T.
AVH map***

Evidence indicates that Pistia stratiotes is native to the Northern Territory and possibly northern Queensland, but introduced in other parts of (mostly eastern) Australia where it has become a weed causing problems in irrigation canals, constructed water-storage dams and natural waterbodies. It can reproduce prolifically, mainly by forming daughter plants on the end of stolons. Rapid expansion forms obstructive mats which interfere with water flow, irrigation and water storage systems, navigation and recreation activities, as well as having habitat and environmental impacts such as reducing biodiversity. See also Weeds in Australia profile compiled by P.G. Kodela (2007).

Text by A. Hay (1993); revised by P.G. Kodela (Feb. 2008)
Taxon concept: Flora of NSW 4 (1993)

APNI* Provides a link to the Australian Plant Name Index (hosted by the Australian National Botanic Gardens) for comprehensive bibliographic data
***The AVH map option provides a detailed interactive Australia wide distribution map drawn from collections held by all major Australian herbaria participating in the Australian Virtual Herbarium project.
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