Water Hyacinth, Eichhornia crassipes & Water Lettuce, Pistia stratiotes – Ecological Profile

Written by: Reid Van Kuren & Andrew Base

Water Lettuce, Pistia stratiotes

Distribution:

Water lettuce is extremely persistent, having found its way into nearly all tropical and subtropical fresh waterways. There is still some debate in the scientific realm regarding its origins. While many experts believe Water Lettuce comes from South Africa, others suggest Central America, Australia, and even the state of Florida (Evans, 2013). Currently, Water Lettuce can be found in pockets and waterways globally. Figure 1 provides a visual for the global distribution. Figure 2 illustrates the invasive distribution within Ontario specifically. (Kaufman, 2017).

water-lettuce

Habitat:

Water lettuce is known for haunting lakes and slow moving streams and rivers around the globe. According to various sources, it exists mainly in warmer climates, however can withstand water temperatures as low as 15◦C. Water Lettuce therefore appears to be absent in Polar Regions and the 50th parallel north.

Reproductive Strategy:

Water lettuce grows floating on the surface of water and has a rather dense and aggressive root system. This invasive species is not complicated; primarily needing its favoured warm climate, oxygen, and to find purchase for its roots. Once this occurs, it will reproduce using very tiny seeds contained in its leaves. Water Lettuce can reproduce both sexually and asexually. As with most species, a male and female plant simply need to be close enough to begin the process of germination. Otherwise, asexual reproduction can occur, and Water Lettuce will generate smaller side plants extending from the side of the mother plant – connected by a short stolon (Giammarco, 2004). A table has been provided below to compare Water Lettuce with the similar invasive species: Water Hyacinth, and associated reproductive strategies used by multiple species.

Habitat:

Water lettuce is known for haunting lakes and slow moving streams and rivers around the globe. According to various sources, it exists mainly in warmer climates, however can withstand water temperatures as low as 15◦C. Water Lettuce therefore appears to be absent in Polar Regions and the 50th parallel north.

Reproductive Strategy:

Water lettuce grows floating on the surface of water and has a rather dense and aggressive root system. This invasive species is not complicated; primarily needing its favoured warm climate, oxygen, and to find purchase for its roots. Once this occurs, it will reproduce using very tiny seeds contained in its leaves. Water Lettuce can reproduce both sexually and asexually. As with most species, a male and female plant simply need to be close enough to begin the process of germination. Otherwise, asexual reproduction can occur, and Water Lettuce will generate smaller side plants extending from the side of the mother plant – connected by a short stolon (Giammarco, 2004). A table has been provided below to compare Water Lettuce with the similar invasive species: Water Hyacinth, and associated reproductive strategies used by multiple species.

Survivorship:

Water Lettuce features a Type II survivorship curve. It reproduces relatively quickly, but does not face many threats or obstacles to growth. This is also why it is considered a pest plant.

Dispersal/Vectors:

Water Lettuce has a very simple life and set of functions. It doesn’t move, nor require it. When the plant is ready, it releases its seeds into the water. The seeds are often carried by the current, take root as a sister plant, or will be consumed by animals, and carried to other aquatic locations and deposited. If conditions are favourable, it will grow.

Special Considerations:

  • Water Lettuce is a very real threat to native vegetation and fish as it can multiply quickly, and cover up fresh water bodies (up to 1,000 rosettes per square meter). This in turn blocks out the sun, killing off aquatic organisms, which then reduced oxygen to minute levels.
  • Despite being banned in numerous states, Water Lettuce is found in thousands of garden supplies around the world, and is kept in both isolated and public water bodies by botanists to manage nutrient levels, or provide shade. (Batcher, 2000).

 


 

Water Hyacinth, Eichhornia crassipes

Distribution:

Much like Water Lettuce, Water Hyacinth is said to have originated in and prefers the climates tropical and subtropical areas. Invasively; the plant is found around the Gulf of Mexico, the warmer more southern areas of the United States, and pockets of Southern Ontario, Canada. (Chace, 2013).

water-hyacinth

Habitat:

As mentioned, Water Hyacinth prefers warm, humid climates. While it can still function in more dry areas (as long as it has water), the temperature shouldn’t fall below 12◦C. It will typically establish itself in nutrient rich waters, and is most successful in still and shadow waters. (Washington, 2014).

Reproductive Strategy:

The reproductive strategy for a Water Hyacinth is relatively simple. It’s a free-floating plant that can expand to form massive mat-like structures through asexual and sexual reproduction. It matures quickly, develops seeds quickly, and the seeds germinate quickly. By generally sticking together though, the plants can guarantee successful offspring since the proper conditions and nutrient requirements will be met. Please see Table 1 for a comparison with Water Lettuce and other strategies.

Survivorship:

Water Hyacinth adopts a Type II survivorship curve. It has a steady reproduction rate, growth rate, and mortality rate. The plant has a small mortality rate compared to its reproduction. It produces thousands of seeds at a time. Their lifespan is relatively short.

Dispersal/Vectors:

The Water Hyacinth allows itself to be carried along slow moving waters as it grows and develops attached sister plants. Each plant has the ability to disperse up to 5,000 seeds in a similar fashion to Water Lettuce. The seeds can be carried by water currents, animals, and the wind to a suitable area. Water Hyacinth mats can also break apart and spread out that way by “splitting up” and continuing their processes over any aquatic area which meets its needs (Kaufman, 2007).

Special Considerations:

  • Considered ornamental, and is therefore sold in nurseries and department stores across North America.
  • Its leaves regrow after moderate freezes. Populations can double in as little as six days.

 

References

Batcher, M. (2000). Element stewardship abstract for Eichornia Crassipes. The Nature                      Conservancy.

Chace, T. (2013). Eradicate Invasive Plants. Timber Press.

Evans, J.M. 2013. Pistia stratiotes L. in the Florida Peninsula: biogeographic evidence             and conservation implications of native tenure for an ‘invasive’ aquatic plant.            Conservation and Society 11(3):233-246.

Giammarco, T. (2004). Water Lettuce & Growth. Aqualand Factsheets.

http://aqualandpetsplus.com/Pond,%20Water%20Lettuce.htm

Kaufman, S.R. (2007). Invasive Plants: Guide to Identification and the Impacts of         Control of Common North America Species. Stackpole Books.

Washington. (2014). Non-Native Freshwater Plants. Water Hyacinth.

http://www.ecy.wa.gov/programs/wq/plants/weeds/hyacinth.html

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