How2Day: Aquatic Stem Plants

Aquatic stem plants are a group of plants with a similar growth pattern. They produce long stems, many times reaching dozens of feet long, that grow leaves but very few branches. They are primarily supported by water buoyancy rather than by the stem, which is very brittle. When the stem breaks, the freed portion becomes a new plant. These plants are popular in aquariums and usually need bright light and heavy trimming to look their best.

Water wisteria (Hygrophila difformis) is a popular and commonly grown stem plant native to southeast Asia. It is grown for its lace-like, deeply cut, light green leaves at nodes along a thin and brittle green stem. The roots sprout from the same nodes as the leaves and form a tangled mass in the water and will also root in the substrate.

Water wisteria likes bright light but will grow in medium light conditions, with at least two watts of fluorescent light per gallon of water in the tank. It does not need carbon dioxide fertilization, but does much better with it. It benefits from iron fertilization but will otherwise survive normal tank conditions. Water wisteria will grow in acidic water down to a pH of 5 and up to 8.

Fanwort (Cabomba caroliniana) is native to the American southeast and is a longtime favorite in aquariums and ponds. It can form large masses outdoors in sunny areas or serve as a backdrop and fish breeding habitat in the aquarium. It has a branched, thin brittle stem with needle-like, fan-shaped leaves in whorls that are three-quarters of an inch wide. It will grow long roots and attach itself to the substrate but can also be grown floating.

Fanwort likes very bright light with at least three to four watts of fluorescent light per gallon in the aquarium. It likes temperatures on the cooler side and will start to suffer if temperatures reach above 78 degrees. It can survive cold temperatures and has become invasive in New England, where it spreads and chokes out native plants.

Dwarf Rotala (Rotala rotundifolia) is one of the easier to grow, red-colored stem plants for the aquarium. It is also popular in water gardens where it can grow above the surface and flower. It has a slender stem and small oval leaves that reach about a quarter of an inch long. New growth is red and fades to green as it ages.

Dwarf rotala needs high light to produce red leaves but will grow in medium light similar to water wisteria. It is adaptable to many types of water conditions but likes temperatures to be in the mid 60s to the mid 80s. It can tolerate a wide range of pH from 5 to 8.

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