Utricularia is a semi-aquatic carnivorous plant that can grow in the terrestrial or aquatic environment. There is another exotic aquatic carnivorous plant, Aldrovanda vesiculosa. It is first observed in India in the sixteenth century. It is a true aquatic carnivore in the family of Droseraceae that is believed to be a direct relative of the Dionaea muscipula, the Venus flytrap due to its snap trap that is similar to that of Venus flytrap. They are widely distributed and scattered in Europe, Africa, India, Australia, and Japan. In Australia, there are two “red” strains of Aldrovanda which are very popular among growers.
It is a fascinating aquatic plant commonly known as the waterwheel plant which is found in acidic ponds and lakes throughout the world. This aquatic plant is a floating plant that is just below the surface of the water. The air containing traps are found to give the plant buoyancy in the water. It enters the dormancy period as tightly rolled turion buds in temperate areas during winter, whereas, they grow all-year-round in tropical countries. This waterwheel is rootless and has about four to six inches long stem. It keeps itself within the range of length with permanent apical growth at the growing end while the other dies away through gradual aging and decomposition. The leaves are connected with a broad petiole that ends in a small trap arranged in whorls of six to nine traps per node, thus giving waterwheel structure, the common name. It also commonly called a waterbug trap. It produces single and small petal flowers that are white in color that appears above the water surface during summer.
It would be challenging to cultivate this waterwheel! This is because Aldrovanda requires a high quality of dissolved carbon dioxide in the water produced by other water plants they grow with them. Other aquatic plants such as rushes (Juncus spp.), sedges (Carex spp.), cattails (Thypha) can be in pots nestled into the peat at the bottom of with the roots planted into the aquarium soil in an aquarium tank. Extra horticultural care is needed to cultivate this species as the water level (six to twelve inches) should not getting much deeper as Aldrovanda float along the shallow edges of ponds in nature. It can adapt to pH range 4.0-7.8 but it prefers slightly acidic water at pH 6.0-7.2 which is found difficult for growing other aquatic plants with it as others might not tolerate acidic conditions. It is better to add a specific concentration of humic acids in the range from one to six-milligram per liter.
High biomass of dead and partly decomposed plant litter can be added to the aquarium tank. This is because the litter is found to be useful in carbon dioxide release and the humic acids decrease the pH value. Alternatively, a carbon dioxide pump can be installed and pump carbon dioxide into the shallow aquarium tank to keep this fellow survives! Algae control can be done by employing water fleas, mosquito larvae, and even tadpoles which feed on algae that growing on the plants. To propagate this plant, cutting can be done by breaking or cutting the internode of the plant to multiply it. It can be bred sexually through cross-pollination to produce viable seeds as self-pollination in culture is unknown. Furthermore, growers should grow this Aldrovanda species in transparent water where it can be fully irradiated by the sun resulted in both high light conditions and high water temperatures. The water temperature is advised to maintain above sixteen degrees Celsius with an optimum range from twenty-three to twenty-six degrees Celsius. This is because a high temperature is necessary for fast growth. The enhancement of the spreading potential of this carnivorous aquatic plant is to ensure there is water flow at every single site of the waterwheel plants. A chain of shallow standing waters should be set up to surround the potential growth site of Aldrovanda.
This semi-circular in shape and a tiny trap is 1/12 inch looks like a translucent green clamshell. As similar to that of Venus flytrap, it has numerous tiny hooked teeth along the margin of each lobe. The trap is surrounded by long and pointy bristles which are hypothesized to prevent the trap from being damaged by other physical objects such as other aquatic plants as this plant is floating freely in the water. This tiny trap has a complex structure that similar to Venus flytrap although it grows fully in the water. Abundant long and filamentous trigger hairs are found in the trap which could be around forty hairs per trap!
There is no known reason for the luring mechanism yet, but the traps are liberally peppered with digestive glands that trap tiny swimming creatures such as water daphnia and eelworms. The preys enter the trap for unknown reasons. It may because of the water flow as in the preying mechanism of aquatic Utricularia in nature. Once the prey had touched the inner hair, the traps close quickly regardless of the number of hairs the prey touched. The tiny teeth aligned on the margin of the lobe will interlock thus imprisoning the prey like that of a Venus flytrap. The trap of the waterwheel squeezes slowly from the margin thus pushing the prey to the base of the trap that near to its hinge and expels most water at the same time. The reason to expel water may because water may dilute the digestive juices. The trap is then sealing itself with a viscid secretion before the digestive enzymes and acids are secreted. Each trap is so powerful until it can catch several meals.
However, it has become endangered species on the International Union for Conservation of Nature (IUCN) Red List and extinct in the wild due to pollution primarily eutrophication. Eutrophication is a phenomenon of algal bloom as a result of the enrichment of the water by minerals and nutrients. The sewage that is high nitrate or phosphate-containing detergents or fertilizers caused the drastic increase of phytoplankton that resulted in insufficient sunlight and an increase in biological oxygen demand (BOD) in the aquatic system. The conditions caused by eutrophication were found not preferred by Aldrovanda thus causing it became an endangered species. Therefore, research and measurements on germplasm conservation should be taken to conserve, protect, and multiply Aldrovanda before it is too late.
Adamec, L. (1995). Ecological requirements and recent European distribution of the aquatic carnivorous plant Aldrovanda vesiculosa L.—A review. Folia Geobotanica, 30(1), 53-61.
Pietropaolo, J., Pietropaolo, P. A., & James. Pietropaolo. (1999). Carnivorous plants of the world. Timber Press.
Meyers-Rice, B. (2006). Growing carnivorous plants. Timber Press.
D’amato, P. (2013). The savage garden, revised: Cultivating carnivorous plants. Ten Speed Press.
Ellison, A. M., & Adamec, L. (Eds.). (2018). Carnivorous Plants: physiology, ecology, and evolution. Oxford University Press.
