Vallisneria spiralis
Vallisneria spiralis, also known as straight vallisneria, tape grass, or eel grass is a common aquarium plant that prefers good light and a nutrient rich substrate. In the wild, it can be found in tropical and sub-tropical regions worldwide. Overview. It has narrow, linear leaves that range in colour from a pale-green to reddish up to 3 feet (1 m) long and up to 0.75 inches broad. "V. spiralis" is monoecious with flowers carried on long spiral stalks that break away from the plant and float on the water's surface. Seeds have not been observed  germinating in aquaria. Instead, it most often propagates by runners which can lead to dense stands. One form of this plant has been described: "V. spiralis" f. "tortifolia", which has also been elevated to the species level by some taxonomists under the name "V. tortissima". The form has tightly twisted leaves. Along with this form, many other trade names have been developed for small variations on the species. Their taxonomic status is uncertain. Invasive species. The species is an effective invader due to its efficient dispersal, vegetative reproduction, high biomass production, and popularity in the aquarium trade. "V. spiralis" is  an "unwanted organism" in New Zealand. It is listed on the National Pest Plant Accord prohibiting it from sale and commercial propagation and distribution. Since 2013 V.spiralis is listed as naturalized alien in Iceland, where it was recorded in geothermal ponds.