Heteranthera dubia

Heteranthera dubia, or water stargrass, is distributed from the southeast of the USA to Central America, in smaller stagnant to flowing waterbodies. There it forms sumbersed populations or floats on the water surface. Floating shoots form yellow flowers with six narrow bracts, which gave this grasslike plant its vernacular name. It is quite undemanding and a fast grower, and has long been known in aquaristics, also under its synonym Zosterella dubia. For a time it had almost disappeared from the hobby, however, in the meantime it is available in trade sometimes, or from other hobbyists.

H. dubia may be a plant that preferrably grows submersed, however, emersed cultivation is also possible. Then it stays smaller and more compact. It is quite similar to its relative, Heteranthera zosterifolia, but grows a bit larger, has longer internodes, and its flowers are yellow instead of blue. It is far more undemanding, which makes it especially interesting for beginning planted tank keepers, fishkeepers and the owners of filterless tanks.

Its single leaves grow 5 to 12 cm long and around 0.4 cm wide. The colour of the water stargrass is light green, and the plant has an inconspicuous grasslike look. Flowers develop mainly when the plant is allowed to float on the water surface under intensive light. The yellow flowerbuds are lifted above the waterline on a 3 to 4 cm long stalk. When the bud opens, the six bracts, three petals and a pistil with stylus become visible.

Z. dubia should be planted in a group. If the plant grows too long and starts floating at the surface, the top shoot can be cut off and re-planted. This is an easy way to propagate it, cuttings of lateral shoots are of course also possible.

H. dubia is also suitable for coldwater tanks and is quite undemanding regarding the water quality. It does ok in soft water, but prefers higher hardness levels. The pH may be in the range of 5 to 8. CO₂ fertilisation is unnecessary but may speed up its rapid growth even further.
During the warm season, Heteranthera dubia also does well out of doors, e.g. in shallow zones of garden ponds or in mobile containers, where its star-shaped yellow flowers are an attractive eyecatcher.