Utricularia graminifolia – the carnivorous foreground plant

by Ole Pedersen, Troels Andersen and Claus Christensen

Utricularia graminifolia (Tropica No 049B) belongs to the most interesting water plants. It is carnivorous and creates an attractive green carpet in the foreground within a couple of months. Utricularia graminifolia may be difficult to start up but once it has gotten a firm grip in the aquarium, it offers a unique experience for the aquarist. The tiny trapping devices may inspire long discussions among family members and friends as carnivorous plants always stimulate people's curiosity.
 
Utricularia graminifolia belongs to the bladderwort family (Lentibulariaceae) and originates in SE Asia where it has been found in the southern China, India, Sri Lanka, Burma, Laos and Vietnam. At those sites, it appears as amphibious swamp plant as well as totally submerged in springs and along small streams. Its natural habitat is often shaded and it rarely grows in full sunlight. It always grew in very soft water where we found it and we had severe difficulties keeping it alive during transportation. Fortunately, the plant that is being produced now is much sturdier and thus, more suitable for use in aquaria but it remains a plant for the specialist. Utricularia aurea is another bladderwort which occasionally is found in the shops but it looks completely different with a growth form similar to species of Ceratophyllum and Myriophyllum.

Bladderworts are all carnivorous plants and many of them are associated with water. The genus name "Utricularia" refers to the bladders (trapping devices) whereas the species name "graminifolia" refers to the grass-leaved leaves. The grass-leaved leaves are exactly what distinguish it from the other approximately 210 species of bladderworts that have been described so far. The tiny grass-leaved leaves form an imbricate structure of freshly green leaves, which normally covers the bladders that are formed on the rhizome and the midribs. It flowers when it grows emerged.
However, what makes Utricularia graminifolia unique to the aquarist is the tiny 2 mm long bladders that in nature traps crustaceans and ciliates seeking shelter among leaves and rhizomes. The animals are digested by enzymes secreted by the into the bladders, and the released nutrients are subsequently taken up by the plant and used to support new growth. Utricularia graminifolia often grows in very nutrient poor environments and thus, it is a huge advantage to be able to explore alternative nutrient sources of particularly nitrogen (N) and phosphorous (P) by trapping nutritious animals.

Tropica grows Utricularia graminifolia emergent and it is supplied on either stone wool or coir discs. When planted in the aquarium, the clod should be divided into 6 to 8 smaller pieces and planted with a distance of 5 cm in the foreground of the aquarium or on a slope in the aquascape. It is important to keep about 1 cm of the coir or stone wool in order to provide good anchoring of the plants. Using tweezers to insert the tiny blocks of plants makes the entire process of planting much easier. To begin with, Utricularia graminifolia should be offered relatively low light but after the initial 6-8 weeks, where after the plants have obtained a firm hold in the aquarium, the light may be increased. At this point in time, the tiny blocks have now been transformed into a continuous grass-like carpet and this is the time where PLANT NUTRITION liquid should be supplied in order to prevent iron and manganese deficiencies. Our experience with Utricularia graminifolia shows that it is doing best at a pH of 6.8 to 7.0 in water of 7-10 dKh hardness. Fertilization with CO2 is not required but if supplied, the growth is stimulated significantly. Although the commercially available variety is sturdier that the wild type, the initial phase after planting may prove critical since the Utricularia graminifolia is sensitive to environmental changes. Thus, make sure that the recommendations are followed and keep other fast-growing plants out of the new patches with Utricularia graminifolia until the plants are well established in the aquarium. Utricularia graminifolia is relatively fragile and thus, it should not be kept with fishes with burrowing behaviour.

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Utricularia graminifolia in its natural habitat on the edge of a shaded stream in southern Vietnam. The plant grows partly submerged and partly emerged among the leaf litter.

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Close-up of the trapping devices on Utricularia graminifolia that are used to catch crustaceans and ciliates. The animals contain nitrogen and phosphorous that can be used by the plant after the tissue has been dissolved by enzymes in the tiny traps. Photo by Oliver Knott.

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Utricularia graminifolia is used in aquascaping where it forms a green stream in the aquarium. The plant may also be used as ordinary foreground plant where it forms a continuous green carpet 6-8 week after planting. Photo by Oliver Knott.