Perfect for naturalizing the margins of wildlife ponds, water stargrass is a petite wetland plant with a slender stature. Also known as grass-leaf mud-plantain or Zosterella dubia, this aquatic perennial may have subtle morphological variations that are dependent on water conditions such as depth and current strength. Plasticity, as a form of adaptability, is shared by many other members of its family of pickerel weeds (Pontederiaceae).
Found as far north as Canada and as far south as Guatemala, water stargrass commonly occurs in the freshwater bodies of North and Central America. It is named for the grass-like form of its foliage, which is typically borne on submerged vegetative stems. The leaves, which grow up to 15 cm (6 inches) long, may also be fully exposed to the atmosphere. These are contrasted by their short-lived, emergent flowers, which are set apart by yellow petals arranged in a star-like formation.
In shorelines experiencing drastic seasonal changes in moisture levels, water stargrass may persist as a seemingly terrestrial or landlocked plant. The blooms on exposed stands are borne on shorter floral stalks. If this species’ stem is mostly buried in sand or soil, its leaves may seem to develop a more basal, rosette arrangement.
Facts, Benefits & Uses of Water Stargrass
Water stargrass can create substantial colonies in shallow and fairly calm waters. This freshwater plant thrives in ponds and lakes, but it may also naturally occur along the banks of rivers and streams. Often mistaken as an undeniably dainty wildflower through its bloom period of July to October, it is no stranger to muddy shorelines throughout its native range. Recreational anglers in the US will have likely trampled a few of its natural stands!
Like many other emergent aquatic plants, the self-spreading root system of water stargrass can aid in enhancing the stability of a water feature’s shores or banks. Given its tendency to grow quite quickly in optimal conditions, it is resilient enough to recover from mild foot traffic, grazing, or even damage from boats. Despite its morphological plasticity and rapid growth, however, many of its natural colonies are at risk of being extirpated due to the degradation of water quality in their habitats.
The stems of water stargrass may be rooted into substrates that are found at depths of up to 5.5 meters (18 feet). Only those that can grow towards the surface, typically in shallower zones, can produce inflorescences. Direct light is usually required for the production of swathes of blooms. Equipped with inflated stamens, these attract a range of aerial pollinators. The submerged leaves may occasionally be consumed by wildlife.
Water Stargrass Growth, Hardiness & Climate
The stems of water stargrass are able to remain upright in a few feet of calm water. Once they reach the surface, they may continue to elongate horizontally. Interestingly, the densest colonies are found in conditions where the stems are unlikely to reach the surface and produce their blooms. Cleistogamous flowers may develop underwater, but these do not open and, as a result, cannot be cross-pollinated. Though they do not expose their stamens and remain enclosed by specialized leaves throughout their life, these “closed” underwater blooms are still able to produce seeds.
Alkaline conditions encourage the rapid growth of water stargrass stems in cool waters. Well-established stems may thrive in fast-flowing waters, where their leaves remain oriented in the direction of the current. They may also persist in sluggish waters as long as pH levels are optimized and the stems can access direct sunlight. This undemanding species tolerates a wide range of temperatures and depths, but note that exposed blooms are often restricted to shallow backwaters or muddy banks.
How to Plant Water Stargrass
As an emergent or shoreline plant for wildlife and backyard ponds, water stargrass is usually grown using its cuttings. Fragments of its stems or root divisions attached to healthy shoots can be propagated in a straightforward manner. These can be planted in either controlled indoor conditions or directly into their permanent outdoor positions. Indoors, a setup with a few inches of standing water should suffice. You may also grow this species in a well-lit tank.
The best water temperatures for growing water stargrass range between 15 – 27˚C (59 – 81˚F). This means that both cool and warm-water tanks can be used to quickly produce well-rooted specimens. Soft water, with relatively high KH levels, supports rapid growth. Additionally, slightly alkaline pH levels should encourage the spread of highly productive stems.
In setups with a few inches to about a foot of water, the stems may quickly rise to the surface. These can be cut back to maintain their height. The new cuttings can then be planted in their own pots and allowed to grow in the same manner as their parent plants. Those placed along pond shorelines may be restricted to baskets or submerged pots. Note, however, that these may spread to other parts of the pond via fragmentation. The cleistogamous blooms may also distribute seeds around the pond, causing stargrass seedlings to arise everywhere.
How to Care for Water Stargrass
Apart from the general maintenance of its stems, water stargrass requires little in terms of care. Its well-established colonies should be trimmed regularly to prevent them from creating dense mats of foliage. When left to elongate, keep in mind that the stems may create flooding thickets, blocking out light. Simply cut these back once they have grown too long for your pond setup, and make sure to dispose of the cuttings properly.
Heteranthera dubia is prone to being infected by Membranosorus heterantherae – a fungus with a parasitic mode of spread. Infected plants tend to possess both nodal and root galls. Some of these galls become rich in nitrogen and may contain a high amount of calcium oxalate crystals. They may attract the aquatic larvae of some insects. The clusters of herbivorous larvae may affect plant growth by compromising the health of both shoots and roots. You may opt to remove infected specimens through manual means, but note that a small number of galls should not significantly affect plant survival.
How to Winter Water Stargrass
As temperatures drop, water stargrass stems may naturally break into fragments and eventually settle onto the bottom of a water feature. Specimens that are fully exposed to the elements may die back completely in regions experiencing frosts and markedly low temperatures. The fragments that overwinter within a pond are usually able to produce new tissues in spring. These rapidly regenerate into mature plants, creating complex underwater structures within just a few months.
If you wish to ensure that your water stargrass stands do not die back during winter, you may transfer them into a temperature-regulated and well-lit tank. As long as conditions are optimized, the shoots should continue to remain productive. You may also move pots or containers of this species into a greenhouse. Ensure that they remain at least partly submerged through the season. Come spring, remove all decaying stems and leaves before returning the pots to their original positions.
Is Water Stargrass Invasive or Toxic?
Water stargrass is non-toxic, but it may exhibit a pest-like mode of spread in ponds where it has little competition. Its sprawling stems can dominate shallow shorelines, preventing other emergent species from obtaining the necessary light levels and space for expansion.
Though controlled densities of this species are generally beneficial, overgrown colonies can be somewhat problematic in natural basins with slow currents, alkaline water conditions, and full exposure to direct sunlight. These can exhaust freshwater systems of the necessary resources to support a high diversity of aquatic macrophytes. To prevent harmful impacts on fish populations and plant health, widespread colonies need to be managed via a combination of chemical, mechanical, and biological means.
Is Water Stargrass Edible? Do Animals Eat It?
Although it can be consumed without harm, Heteranthera dubia is not necessarily considered a valuable food source in ponds. When other macrophytes are scarce, however, you’ll find that waterfowl and herbivorous fish may feed on its grass-like leaves. Nonetheless, its presence is associated with a rich diversity of food choices for fish as its shoots are often home to a wide range of small invertebrates.
Where to Buy Water Stargrass & Seeds? (UK & US)
Though H. dubia is a US native and can readily be found in the wild, it can be quite difficult to find in plant nurseries and aquarium shops. It is the less common cousin of H. zosterifolia (non-native), which is frequently carried in aquascaping stores. When it does happen to be available, it is usually sold as plug plants that are ready to be situated directly into an outdoor pond or indoor tank.
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