An ornamental pond, basin of water on a table or a large aquarium can support plant growth without any need for soil. Often these aquatic plants are referred to as floating plants or oxygenators since they release oxygen into the water to the benefit of fish or amphibians. Generally speaking, the warmer the water and more light received, the faster these plants grow. Use caution; some species grow rapidly and become weedy or are prohibited for use in outdoor water bodies, as they are ecologically invasive.
Also called frog's buttons, duckweed (Lemna spp.) comprises 13 different species of tiny-leaved plants that grow on the surface of motionless freshwater. The small leaves are often eaten by fish as well as waterfowl.
Growing rapidly in hot temperatures, mosquito fern (Azolla spp.) will cover the entire surface of the water if never harvested or killed by cold winter temperatures. The leaves are small but frothy looking, resembling a feathery texture of a tiny fern.
Beloved for its spike of lavender-blue flowers, the water hyacinth (Eichhornia crassipes) is also an invasive weed in many lakes, canals and ponds in regions that don't experience freezes during the winter. The rosettes of oval, waxy leaves and network of stems and buoyant air "bulbs" grow quickly to create a thicket of foliage atop the water.
Potentially as weedy as water hyacinth in warm climate regions, the water lettuce (Pistia stratoides) rapidly grows into attractive mats of light green on the water surface. The leaves form a rosette that look like a leafy head of vegetable lettuce. It is killed by winter frosts and freezes.
Ten species of salvinia fern (Salvinia spp.) float on freshwater surfaces around the world, and many are noxious weeds in southeastern Africa or southern India, according to "The Practical Rock and Water Garden." The light-green leaves are soft to the touch and are covered in silky hairs. In cold temperatures, the leaves blush yellow or bronze-orange.
Curly Water Thyme
Once known by the botanical name Elodea crispa, curly water thyme (Lagarosiphon major) grows long, curving stems lined with tiny green leaves that are submerged just below the water's surface. This popular plant for freshwater aquariums supplies food to fish as well as a breeding habitat and cover for hatched fry. There are nine species of curly water thyme native to tropical Africa.
Another submerged plant, hornwort (Ceratophyllum spp.) lacks roots and is well-suited to freshwater that is chilly or shaded from warm sunlight. There are 30 species in the world, and all can be propagated by shredding the stems, each of which will rejuvenate into new masses of long stems with eyelash-like tufts of green leaves.