Monday, October 15, 2012

Water Lettuce is never eaten by Water Cows

Species name: Pistia stratiotes

Common name: water lettuce

Location: Ontario

The origins of water lettuce are unknown, but this plant was first discovered in Africa near Lake Victoria. It's presumed native to that location, but it could have been introduced there previously. It is now present in just about every waterway in tropical and subtropical area around the world, either through accidental human introduction, purposeful human introduction, or natural spread. It has become dangerously invasive in areas that don't have sub-zero temperatures during the winter, since it is not cold tolerant. Thankfully, this means that we have mostly escaped in Canada from having to worry about this long-term; with milder winters there is the serious threat of this absolutely taking off.

This is a very popular backyard pond aquatic plant, since it is better at competing for resources than algae that usually takes over a pond. Should a pond be properly balanced, the chance of algae being able to take over a pond is actually slim to nil. Over-feeding fish, having too many fish, too many plants, not enough water aeration, and a pond that is too shallow can all lead to a biological imbalance, which can in turn lead to an algal domination.

This plant has been especially successful at dominating waterways in Florida, where it has been contributing to the mosquito population boom. Mosquitos require standing water in order to lay their eggs, as their larvae are aquatic. Laying eggs under the surface of the bottom leaves of water lettuce provide the developing eggs with a sheltered environment, and provide the newly hatched larvae with a safe place to develop after hatching. The larvae actually create a siphon tube from where they live on the root of the plant up to the surface of the water so that they can get oxygen. A neat adaptation, but one that makes it incredibly difficult to control mosquito populations where water lettuce is abundant.