- Laitue d'eau,
- Nile cabbage,
- Water lettuce
Pistia stratiotes L.
Pistia - pistos means aquatic
P. stratiotes is an aquatic herb, floating, without stem, consisting of a rosette of leaves, 5 to 25 cm in diameter and short stolons giving rise to daughter plants. A large network of fibrous roots hanging in the water. The leaves are in dense rosette, sessile arranged, broadly spatulate shape, fleshy, consisting of tissue floating very hairy. Both sides are hairy, grayish-green or yellowish. The flowers are numerous, small and hidden at the base of leaves, surrounded by a small room pale green or white leaf-like long by 7 mm. The fruits are small, elongated bays 6 to 10 mm long, containing several seeds dark.
Cotyledons are rounded or obovate, scarcely stalked, spread on the surface of water 1 to 2 mm in diameter. No petiole, covered by hairs.
First leaves are simple, alternate, sessile, highly hairy.
P. stratiotes is a floating plant, drifting, without stem, consisting of a rosette of leaves, 5 to 25 cm in diameter and short stolons giving rise to daughter plants.
Roots are fibrous, many fibrous roots, pendulous, measuring up to 50 cm long.
Stem is tillering indistinct at the base of the leaves. Presence of lateral stolons from the base of the leaves, cylindrical 1 to 5 mm in diameter.
Leaves are simple, alternate, sessile and spongy, dense spiral rosette. The blade is spatulate, obovate with a round to truncate and cuneate base, 6 to 12 cm long and 3-6 cm wide. The are 5 to 7 (13) subparallel veins, prominent on the lowersurface. The upper surface is green and tomentose while the lower surface is paler and denser tomentum. Blade is densely covered with hairs.
Inflorescences are small, hidden by leaves, carried by a very short stem, about 4 mm long. It consists of a white long spathe 5-25 mm, persistent, glabrous to tomentose inside and outside, forming two cavities.
Flower are small, green, within the leaves. Female flowers are in the lower cavity, without perianth and 2-8 apical. Male flowers are in the upper cavity, inserted in a whorl axis subtended by a shallow cup. The male flowers are reduced by two stamens attached. The female flower is solitary, reduced to an ovoid unilocular ovary, inserted through the axis of the spadix, with a box containing several ovules sessile. Flowering in December to June.
Fruits are ellipsoid, berry, 6 to 10 mm long and 3-6 mm wide, thin-walled, containing 4-12 seeds.
Seeds are ovoid or oblong, about 2 mm long and 1 mm wide at the top cut off and depressed disc-shaped. Testa rough, dark brown.
P. stratiotes is an aquatic plant that propagates by seeds or by vegetative spread by issuing many runners. When the old leaves rot, fruit fall and sink to the bottom where they eventually decay, releasing the seeds. Once there is light, the seeds germinate on the bottom. This species has a very rapid growth patttern. It doubles its biomass every 10 to 15 days depending on water temperature and nutrient content.
It occurs in stagnant water, river with low current, lakes and canals.
Distributed in the North East and Eastern part of South Africa along the boundries.
It can be harmful to aquatic plants such as watercress and wildlife living in aquatic environments. resulting in serious ecological consequences, particularly for aquatic life by acidification, reduction of oxygen in the water, eutrophication by decomposition mass of old leaves.
Declared as category 1, prohibited weed. It is an invasive weed. It disturbes watercourses and provide habitat for mosquitoes and bilharzia-carring snails.
P. stratiotes is an invasive weed with high impact on the aquatic ecosystem.
It can be controlled by mechanical and hand removal method and terbutryn herbicides has been registered as a chemical control.
(AdventOI) Le Bourgeois, T., Carrara, A., Dodet, M., Dogley, W., Gaungoo, A., Grard, P., Ibrahim, Y., Jeuffrault, E., Lebreton, G., Poilecot, P., Prosperi, J., Randriamampianina, J.A., Andrianaivo A.P., and Théveny, F. (2008). Advent-OI: Principales adventices des îles du sud-ouest de l'Océan Indien. Cirad. Montpellier, France, Cirad. (Problem plants of South Africa) Bromilow, C. (2001), Published by Briza Plublications CC