Family: Araceae
Pistia is a genus of aquatic plants in the arum family, Araceae. It is the sole genus in the tribe Pistieae which reflects its systematic isolation within the family. The single species it comprises, Pistia stratiotes, is often called water cabbage, water lettuce, Nile cabbage, or shellflower. Its native distribution is uncertain but is probably pantropical; it was first discovered from the Nile near Lake Victoria in Africa. It is now present, either naturally or through human introduction, in nearly all tropical and subtropical fresh waterways and is considered an invasive species as well as a mosquito breeding habitat. The genus name is derived from the Greek word πιστός (pistos), meaning "water," and refers to the aquatic nature of the plants. The specific epithet is also derived from a Greek word, στρατιώτης, meaning "soldier," which references the sword-shaped leaves of some plants in the Stratiotes genus.
Pistia stratiotes is a perennial monocotyledon with thick, soft leaves that form a rosette. It floats on the surface of the water, its roots hanging submersed beneath floating leaves. The leaves can measure 2 – 15 cm long and are light green, with parallel venations and wavy margins. The surface of the leaves is covered in short, white hairs which form basket-like structures that can trap air bubbles and increase the plant's buoyancy. The spongy parenchyma with large intercellular spaces in the leaves also aids the plant in floating. The flowers are dioecious, lack petals, and are hidden in the middle of the plant amongst the leaves. Pistia stratiotes has a spadix inflorescence, containing one pistillate flower with one ovary and 2 - 8 staminate flowers with two stamens. The pistillate and carpellate flowers are separated by folds in the spathe, where the male flowers are located above the female flowers. Oval, green berries with ovoid seeds form after successful fertilization. The plant undergoes asexual reproduction by propagating through stolons, yet evidence of sexual reproduction has also been observed in the ponds of Southern Brazil.
Pistia stratiotes are found in slow-moving rivers, lakes, and ponds. The species displays optimal growth in the temperature range of 22 - 30 °C, but can endure extreme temperatures up to 35 °C. As a result, Pistia stratiotes do not grow in colder temperatures, beyond the tropics of Cancer and Capricorn. The species also require slightly acidic water in the pH range of 6.5 - 7.2 for optimal growth
The center of origin of Pistia stratiotes remains uncertain. However, the plant is thought to be native to South America or Africa. Described in Egyptian hieroglyphics and reported by Greek botanists, Dioscorides and Theophrastus, in the Nile River, the plant suggests an African origin. In addition, the co-evolution of Pistia stratiotes with various insects native to Brazil and Argentina, such as the water lettuce weevil, proposes a South American origin. It is a common aquatic plant in the southeastern United States, particularly in Florida. A more recent argument for nativity in Florida notes that it was recorded by botanist, William Bartram, in the St. Johns River basin in 1765, and fossil specimens dating back to the late Pleistocene (~12,000 BP) and early Holocene (~3,500 BP) period are reported from Florida. Yet, the rationale of southeastern, North American nativity remains controversial as disagreeing botanists claim the Spanish may have indirectly introduced into the plant into Florida's basins from their ship ballast. From Wikipedia, the free encyclopedia
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