Pistia stratiotes L.

Water Lettuce; Water Bonnet

Herb

Perennial

Vascular

Water Lettuce is an introduced aquatic perennial in the Arum family (Araceae). It occurs in tropical and warm temperate areas throughout the world. The native range of Water Lettuce is uncertain. It is currently thought to be native from southern Florida and Texas, south to South America. It is depicted in Egyptian hieroglyphics and was reported by the Greek botanist Theophrastus (371-287 BC) from the Nile river area of Africa, possible indicating that it was also native to that area. Water Lettuce occurs in ponds and lakes, in canals, in drainage ditches, and in slow moving streams and rivers. It is also widely cultivated as an ornamental. Water Lettuce is a free-floating herbaceous aquatic perennial. The leaves form a compact floating rosette with a dense mass of feathery roots extending down into the water. The leaves are sessile, obovate to spatulate in outline, densely pubescent, with entire margins. The apex of the leaf is rounded or notched. The leaves are grayish-green above and lighter green below. The veins are raised on the lower surface of the leaf. Water Lettuce reproduces primarily by forming short stolons that end in a plantlet. Flowers are produced on short peduncles from the axils of the leaves. The inflorescence consists of a pubescent, tubular green spathe that surrounds the flowers. The spathe is closed at the base and open at the top. The flowers are unisexual in a spadix. The single female flower is terminal on the spadix with several male flowers below. The greenish flowers lack a perianth. The fruit is a greenish berry with 4-10 seed. Water Lettuce is a serious pest in many areas of the world. It clogs waterways and serves as a breeding site for mosquitoes and other insects. A South American beetle (Neohydronomus affinis) and Asian moth (Samea multiplicalis) feed on the plants and have been used as biological control agents.—A. Diamond.

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Not Native OBL (NWPL) G5 (Global Rank)

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