Little star

The Planted Tank
By Robert Paul Hudson

Star light star bright


“I got this strange looking plant from my club auction. The leaves are wavy edged and the whole plant is shaped like a star and as big around as a quarter. The plant is labeled as ‘Downoi‘. I can not find this plant in any of my books. Is this a true aquatic plant, and do you have any information about it?”

this is Pogostemon helferi emersed, above is the same plant grown underwater




Making of a star

The plant you are referring to is Pogostemon helferi, and was discovered in Thailand where it was given the name “dao noi” which means “little star”. Somehow the Thai name has been represented by the word downoi to look like an English word instead of translating the meaning of the word.

P. helferi is a plant that goes thru a drastic transformation, no less remarkable than a caterpillar morphing to a butterfly. In shallow, muddy wetlands, it grows long stems with tiny almond shaped leaves. When submersed underwater, each small leaf turns into a four or five point star. Roots form at the base. Under intense light in the aquarium, each star grows larger but retains its shape. Under lower light levels a stem forms in the center of the star and grows toward the water surface and above, reverting back to its prior form.

Both growth forms have recently become commercially available. The emergent growth form is usually potted. Either lay the stems horizontal across the substrate or plant the stems upright. It will take about thirty days or less depending on the light intensity for the metamorphosis to begin. Once the stars have formed, cut each off the stems and plant in rows or groups in the substrate. Make sure they are positioned in an open area that is not over shadowed by other plants.

The submersed growth form may be purchased either potted or bare root, and is usually branched with multiple stars, or growing partially upright and branched. Each star may be removed and planted. Sometimes you may find only one or two stars in a pot that are somewhat grown out.

It appears to do just as well in hard water as soft water, and a pH of 6.0 to 7.5. Other than light, the only other important issue is having a fertile substrate. I would add a fertilizer tablet in the gravel under each plant when first planting. Supplemental C02 will help to speed up growth, but only if the light is adequate.

Other examples

There are other plants that also go thru a radical change when growing underwater. Proserpinaca palustris, known as mermaid weed starts as ovate leaves with saw tooth edges and underwater turns into long, finely denticulated, needle-like leaves. The underwater leaves turn various shades of red, copper, and orange under bright light. It grows quite slowly and needs as much light as you can give it, but it offers an unusual look and somewhat of a challenge. It will transform more quickly if it is in shallow water.

Hygrophila balsimica is another example. Large solid leaves that contain a toxin become deeply grooved almost feathery looking and completely harmless loosing all the toxin.

Why the change

Most aquatic plants can grow both above water and below water. What you may not know is many aquarium plants are grown purposely with only their roots in water by commercial growers to attain quicker and larger growth. When grown this way the plants are less likely to have algae and parasites. Although these plants are true aquatic, they require some time to adapt to growing underwater, and may change in appearance in the process.

Plants will adapt fairly quickly, but may change their leaf structure: shape and size, dramatically. Aquatic plants have a very highly developed system of air cavities or canals. It runs through the entire plant, from the leaves to the outermost tips, and enables the plant to maintain buoyancy in the water. Because the water supports the plants, their stems and leaves have far less supporting tissue or fibers than those of terrestrial plants, so when growing out of the water, or even floating, the leaves and stems become much thicker or wider. When under water, the new growth from these thick stems will be much thinner.

Not all plants that grow with their roots in water are able to make the transition to being fully submersed. These plants are often called “bog plants” or “marginal plants”, and are more suitable for ponds or paludariums.

In nature

In their natural habitat, of the plants we use in our aquarium the greater majority grow emersed, but those submersed plants found in nature do play an important role in the eco system.

The Role of Submersed Aquatic Plants in Waterbodies
· Provides habitat for fish.
· Provides food and habitat for wildlife populations (fish, waterfowl, invertebrates).
· Affects nutrient cycles and other chemical cycles in complex ways.
· Can increase water clarity.
· Stabilizes shorelines and sediments.
· Can increase or decrease dissolved oxygen concentrations, depending on its abundance, the availability of light, and time of day.

The availability of light, water clarity, water depth, and sediment stability affect where submersed plants will grow.

Emersed plants are plants that grow out of the water (or during low-water times, in exposed sediments). They are rooted to the bottom, but their stems, leaves and flowers are above the water. They too provide environmental roles:

Provide habitat for fish.
Provide food (seeds and leaves) and habitat for wildlife populations such as ducks.
Reduce shoreline erosion.

Make an educated choice

Each growth form has its advantages when purchased by the consumer. Emergent growth plants ship better, and are more hardy. Submersed growth plants may be more colorful, but are also more sensitive and delicate. In some cases submersed plants may be more expensive. Some hobbyists may not be patient enough to wait for the plants to adapt to growing underwater and the desire for instant gratification steers them to search for submersed plants. This is why trading between hobbyists has become popular. If you provide optimal conditions for plant growth either growth form will flourish. Observing this change first hand is an education on how life in our world is forever resilient and adaptive.