Stargrass, Heteranthera zosterifolia

By Mary McCaw
From the November 1999 issue of "The Daphnian", Boston Aquarium Society
Aquarticles

About five years ago, I got back into the hobby after an absence of many years. When I was a child, my older brother and I had two planted aquariums in which we grew vallisneria, sagittaria, elodea, cabomba, and Amazon swords, plants that were readily obtainable in our area. I was pleased to discover that nowadays there is much more variety in the commonly available aquatic plants as compared to the early 60's. When I pored over books about aquariums and aquatic plants, one particular plant, stargrass or Heteranthera zosterifolia caught my eye. Stargrass wasn't easy to find. About three years ago I managed to obtain some at one of our Boston Aquarium Society monthly auctions.

What attracted me to this plant? I was impressed by its bright green color and its great beauty. Stargrass is aptly named because its densely tufted crowns on the ends of each shoot resemble a twinkling star. Like elodea and Rotala rotundifolia, it is a stem plant with narrow, lanceolate leaves, but its leaves are longer and are lighter green. Its many leafed crowns further distinguish it from elodea and Rotala rotundifolia. It looks especially star-like when individual stems are planted at different heights.

The books I consulted gave similar information about stargrass. It is native to South America and is found in Northern Argentina, Southern Brazil, Paraguay, and Bolivia. My sources agreed that stargrass requires a pH of 6.0-7.5, a carbonate hardness of 3-15 degrees, and bright light in order to grow well. If the light it receives is bright enough, it will delight the aquarist with small blue flowers. I have found by experience that stargrass will grow in less than ideal conditions. While all the books say that it requires bright light, I have been able to grow it with only moderate light. Although only one of the references I consulted say that it prefers soft water, I suspect that the fact that my water has a carbonate hardness of about 2 offsets the less than ideal light level. Unfortunately, the first time I tried it, I planted it in the foreground of one of my 20H tanks. When it didn't grow well for me and finally died off, I concluded that two 20w fluorescent bulbs weren't enough light for it. Not long afterwards I bought some more at another auction. This time I gave it more light, placing it in my 45 g. "wonder tank." I call it my "wonder tank" because any plant I have ever tried there has done well thanks to the supplemental light it receives from a skylight in addition to three 40w bulbs. My "wonder tank" didn't disappoint me. Finally my stargrass took off! Soon afterwards, I tried short cuttings in the background of my 20L tank. Two 20W tubes provide the lighting. Stargrass flourished for me there, too, because the 20L's shallowness allows light to penetrate the surface well. My success in the 20L tank emboldened me to try stargrass in the background of another 20H. To my surprise, it has flourished there; however, it grows much more slowly. When I compare stargrass's growth in the 45 g. tank with that of the smaller tanks, the difference is that in the stronger light of the 45 g. tank, stargrass is lighter green in color (comparable to pennywort or mayaca) and grows more rapidly. I suspect that in the case of the smaller tanks I am pressing the limits in terms of the amount of light under which stargrass will flourish. Stargrass is brittle and breaks easily. I have found that it is much easier to handle with long-handled tweezers.

So how well stargrass will grow for you depends on several variables, the amount of light you give it, the softness or hardness of your water, and the depth of your tank. The deeper your tank, the more light it will require. You can grow it with or without CO2 as long as your lighting is bright enough. As in the case of other stem plants it should be fertilized with liquid fertilizer made especially for aquatic plants. CO2 fertilization will rapidly increase its growth.

Stargrass is very versatile in that it can be used as a foreground, mid-ground and background plant. The reason for this is that it can be trimmed and shaped just like a hedge. When used in the foreground it should be trimmed to about an inch or so; side shoots will develop below the cutting point and soon you will have a rich, green carpet. In mid-ground stargrass can be used to butt up against other plants, concealing the bottoms of those stem plants with scant leaves. Left to its own devices, it will grow about 20 in. tall, making it suitable for the back and sides.

A particularly effective way of showing stargrass to its best advantage is to plant it in "plant rows" in the manner of the Dutch aquarists. The shortest pieces are in front, and each stem increases in height up to the background in a diagonal line. I have done so in my 45 g. tank, and in my mind, this arrangement makes it twinkle all the more. Avoid, however, starting a row in the middle of your tank since doing so would visually split the tank in half.

When used especially in the foreground and mid-ground, stargrass grows so rapidly that it will need to be trimmed every 2-3 weeks. In my experience, however, unlike in the case of myriophyllum or cabomba, you can let it go several times without replanting the tops. While all the maintenance required may seem like a disadvantage, on the other hand there is nothing like stargrass to quickly cover up bare spots in your tank.

When neglected, the tops of the plant will soon cover the surface of the water and prevent light from reaching the lower parts of the stems. As a result, the bottoms of stems will be bare. If this happens, trim each stem leaving an inch or two bare and replant each stem about 1" apart. This will allow light to reach the bottom of the stem and will encourage branching. Soon you will have a new hedge in no time!

As an aquarium plant stargrass has much to recommend it. It is one of the few aquatic plants that can be grown anywhere in your tank, and aside from its moderate - high light requirements, doesn't need any special care. In our club stargrass is never referred to by its common name and always as Heteranthera zosterifolia. This has always puzzled me. Perhaps the reason has been lack of familiarity. I hope this article leaves everyone better informed. Stargrass is a versatile plant which I encourage you to try.