Water hyacinth

''Pontederia crassipes'' (formerly ''Eichhornia crassipes''), commonly known as common water hyacinth is an aquatic plant native to South America, naturalized throughout the world, and often invasive outside its native range.''Pontederia crassipes''
Kew Royal Botanic Gardens Plants of the World Online. Accessed April 19, 2022.''Eichhornia crassipes''
Kew Royal Botanic Gardens Plants of the World Online. Accessed April 19, 2022.
June 15, 2016. Flora of Bangladesh. Accessed April 19, 2022. It is the sole species of the subgenus ''Oshunae'' within the genus ''Pontederia''. Anecdotally, it is known as the "terror of Bengal" due to its invasive growth tendencies.

Description

Water hyacinth is a free-floating perennial aquatic plant (or hydrophyte) native to tropical and sub-tropical South America. With broad, thick, glossy, ovate leaves, water hyacinth may rise above the surface of the water as much as in height. The leaves are across on a stem which is floating by means of buoyant bulb-like nodules at its base above the water surface. They have long, spongy and bulbous stalks. The feathery, freely hanging roots are purple-black. An erect stalk supports a single spike of 8–15 conspicuously attractive flowers, mostly lavender to pink in colour with six petals. When not in bloom, water hyacinth may be mistaken for frog's-bit ('' Limnobium spongia'') or Amazon frogbit (''Limnobium laevigatum'').

One of the fastest-growing plants known, water hyacinth reproduces primarily by way of runners or stolons, which eventually form daughter plants. Each plant additionally can produce thousands of seeds each year, and these seeds can remain viable for more than 28 years. The common water hyacinth (''Pontederia crassipes'') are vigorous growers and mats can double in size in one to two weeks. And in terms of plant count rather than size, they are said to multiply by more than a hundredfold in number, in a matter of 23 days.

In their native range, these flowers are pollinated by long-tongued bees and they can reproduce both sexually and clonally. The invasiveness of the hyacinth is related to its ability to clone itself and large patches are likely to all be part of the same genetic form.

Water hyacinth has three flower morphs and is termed " tristylous". The flower morphs are named for the length of their pistil: long, medium and short. Tristylous populations are however limited to the native lowland South America range of water hyacinth; in the introduced range, the M-morph prevails, with the L-morph occurring occasionally and the S-morph is absent altogether. This geographical distribution of the floral morphs indicates that founder events have played a prominent role in the species' worldwide spread.

Habitat and ecology

Its habitat ranges from tropical desert to subtropical or warm temperate desert to rainforest zones. The temperature tolerance of the water hyacinth is the following; its minimum growth temperature is ; its optimum growth temperature is ; its maximum growth temperature is , and its pH tolerance is estimated at 5.0–7.5. Leaves are killed by frost and plants do not tolerate water temperatures > . Water hyacinths do not grow where the average salinity is greater than 15% that of sea water (around 5 g salt per kg). In brackish water, its leaves show epinasty and chlorosis, and eventually die. Rafts of harvested water hyacinth have been floated to the sea where it is killed.

'' Azotobacter chroococcum'', a species of nitrogen-fixing bacteria, is probably concentrated around the bases of the petioles, but the bacteria do not fix nitrogen unless the plant is suffering extreme nitrogen deficiency. apud .

Fresh plants contain prickly crystals. This plant is reported to contain hydrogen cyanide, alkaloids, and triterpenoids, and may induce itching.''Medicinal plants of east and southeast Asia.'' By L.M Perry. 1980. MIT Press, Cambridge. Cited in . Plants sprayed with 2,4-dichlorophenoxyacetic acid may accumulate lethal doses of nitrates,''Tropical feeds. Feed information summaries and nutritive values.'' By B. Gohl. 1981. FAO Animal Production and Health Series 12. FAO, Rome. Cited in . and other harmful elements in polluted environments.

Invasive species

Water hyacinth grows and reproduces quickly, so it can cover large portions of ponds and lakes. Particularly vulnerable are bodies of water that have already been affected by human activities, such as artificial reservoirs or eutrophied lakes that receive large amounts of nutrients. It outcompetes native aquatic plants, both floating and submerged. In 2011, Wu Fuqin et al. tracked the results of Yunnan Dianchi Lake and also showed that water hyacinth could affect the photosynthesis of phytoplankton, submerged plants and algae by water environment quality and inhibit its growth. The decay process depletes dissolved oxygen in the water, often killing fish.

Water hyacinth can absorb a large amount of harmful heavy metals and other substances. After death, it will rot and sink to the bottom of the water, causing secondary pollution to the water body, destroying the natural water quality, and may even affect the quality of residents' drinking water in severe cases. Water where water hyacinth grows heavily is often a breeding place for disease vectors (e.g. mosquitoes and snails) and harmful pathogens, posing a potential threat to the health of local residents. On the other hand, water hyacinth can also provide a food source for goldfish, keep water clean and help to provide oxygen.

The invasion of water hyacinth also has socioeconomic consequences. Since water hyacinth is comprised up of 95% water, the evapotranspiration rate is high. As such, small lakes that have been covered with the species can dry out and leave communities without adequate water or food supply. In some areas, dense mats of water hyacinth prevents the use of a waterway, leading to the loss of transportation (both human and cargo) as well as a loss of fishing possibilities. Large sums of money are allocated to the removal of water hyacinth from the water bodies as well as figuring out how to destroy the remains harvested. Harvesting water hyacinth mechanically requires a lot of effort. A million tons of fresh biomass would require 75 trucks with a capacity of 40m^3, per day, for 365 days to get rid of a million tons of water hyacinth. The water hyacinth would then be transferred to a dumping site and allowed to decompose which releases CO₂, CH₄ and nitrogen oxides which would all negatively impact the air quality and contribute to global warming.

Water hyacinth has been widely introduced in North America, Europe, Asia, Australia, Africa, and New Zealand. In many areas, it has become an important and pernicious invasive species. In New Zealand, it is listed on the National Pest Plant Accord, which prevents it from being propagated, distributed, or sold. In large water areas such as Louisiana, the Kerala Backwaters in India, Tonlé Sap in Cambodia, and Lake Victoria, it has become a serious pest. The common water hyacinth has become an invasive plant species on Lake Victoria in Africa after it was introduced into the area in the 1980s.

United States

Introduction into the U.S.

Various accounts are given as to how the water hyacinth was introduced to the United States.

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The claim that the water hyacinth was introduced to the U.S. in 1884 at the World's Fair in New Orleans, also known as the World Cotton Centennial, has been characterized as the "first authentic account", as well as "local legend".

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At some time, versions of the "legend" asserted that the plants had been given away as a gift by a Japanese delegation at the fair. This claim is absent in a pertinent article published in a military engineer's trade journal dating to 1940, but appears in a piece penned in 1941 by the director of the wildlife and fisheries division at the Louisiana Department of Conservation, where the author writes, "the Japanese government maintained a Japanese building" at the fair, and the "Japanese staff imported from Venezuela considerable numbers of water hyacinth, which were given away as souvenirs". The claim has been repeated by later writers, with various shifts in the details. Thus NAS fellow Noel D. Vietmeyer (1975) wrote that "Japanese entrepreneurs" introduced the plant into the U.S., and the plants had been "collected from the Orinoco River in Venezuela", and the claim was echoed along the same gist by a pair of NASA researchers (), who asserted that the souvenir plants were carelessly dumped in various waterways. Canadian biologist Spencer C. H. Barrett (2004) meanwhile favored the theory they were first cultivated in garden ponds, after which they multiplied and escaped to the environs. The account gains a different detail as told by children's story-teller Carole Marsh (1992), who says "Japan gave away water hyacinth seeds" during the exposition, and another Southern raconteur, Gaspar J. "Buddy" Stall (1998) assured his readership that the Japanese gave each family a package of those seeds.

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One paper has also inquired into the role which catalog sales of seeds and plants may have played in the dissemination of invasive plants. It has been found that ''P. crassipes'' was offered in the 1884 issue of Bordentown, New Jersey