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Whorl Grass

Catabrosa aquatica

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Plant Profile

Flowering Months:
Poaceae (Grass)
Also in this family:
Alpine Catstail, Alpine Foxtail, Alpine Meadow-grass, Annual Beard-grass, Annual Meadow-grass, Arrow Bamboo, Barren Brome Grass, Bearded Couch Grass, Bearded Fescue, Bermuda Grass, Black Bent, Black Grass, Blue Fescue, Blue Moor-grass, Bog Hair-grass, Borrer's Saltmarsh Grass, Bread Wheat, Bristle Bent, Brown Bent, Brown Sedge, Bulbous Foxtail, Bulbous Meadow-grass, California Brome Grass, Canary Grass, Carnation Sedge, Cocksfoot, Cockspur, Common Bent, Common Cord-grass, Common Millet, Common Reed, Common Saltmarsh Grass, Compact Brome Grass, Corn, Couch Grass, Creeping Bent, Creeping Soft-grass, Crested Dog's-tail, Crested Hair-grass, Cultivated Oat, Curved Hard Grass, Cut Grass, Dense Silky Bent, Downy Oat-grass, Drooping Brome Grass, Drooping Tor Grass, Dune Fescue, Early Hair-grass, Early Meadow-grass, Early Sand-grass, False Brome Grass, False Oat-grass, Fern Grass, Fine-leaved Sheep's Fescue, Flattened Meadow-grass, Floating Sweet-grass, Foxtail Barley, French Oat, Giant Fescue, Glaucous Meadow-grass, Great Brome Grass, Greater Quaking Grass, Grey Hair-grass, Hairy Brome Grass, Hairy Finger-grass, Hard Fescue, Hard Grass, Harestail Grass, Heath Grass, Holy Grass, Hybrid Marram Grass, Italian Rye Grass, Knotroot Bristlegrass, Lesser Hairy Brome Grass, Lesser Quaking Grass, Loose Silky Bent, Lyme Grass, Marram Grass, Marsh Foxtail, Mat Grass, Mat-grass Fescue, Meadow Barley, Meadow Fescue, Meadow Foxtail, Meadow Oat-grass, Mountain Melick, Narrow-leaved Meadow-grass, Narrow-leaved Small-reed, Neglected Couch Grass, Nit Grass, Orange Foxtail, Pampas Grass, Perennial Rye Grass, Plicate Sweet-grass, Purple Moor-grass, Purple Small-reed, Purple-stem Catstail, Quaking Grass, Ratstail Fescue, Red Fescue, Reed Canary Grass, Reed Sweet-grass, Reflexed Saltmarsh Grass, Rescue Grass, Rough Meadow-grass, Rush-leaved Fescue, Sand Catstail, Sand Couch Grass, Scandinavian Small-reed, Scottish Small-reed, Sea Barley, Sea Couch Grass, Sea Fern Grass, Sheep's Fescue, Silver Hair-grass, Six-rowed Barley, Slender Brome Grass, Small Cord-grass, Small Sweet-grass, Smaller Catstail, Smooth Brome Grass, Smooth Cord-grass, Smooth Finger-grass, Smooth Meadow-grass, Soft Brome Grass, Somerset Hair-grass, Sorghum, Spreading Meadow-grass, Squirreltail Fescue, Stiff Brome Grass, Stiff Saltmarsh Grass, Sweet Vernal Grass, Tall Fescue, Timothy Grass, Tor Grass, Tufted Hair-grass, Two-rowed Barley, Upright Brome Grass, Velvet Bent, Viviparous Fescue, Wall Barley, Wavy Hair-grass, Wavy Meadow-grass, Wild Oat, Wood Barley, Wood Fescue, Wood Meadow-grass, Wood Melick, Wood Millet, Yellow Oat-grass, Yorkshire Fog
Life Cycle:
Maximum Size:
50 centimetres tall
Ditches, water, waterside.

Green, no petals
The flowers are in clusters with branches appearing in distinctive alternating half-whorls. The spikelets are greenish-purple. Each spikelet has 2 florets. Pollinated by the wind.
The seeds ripen from July to September.
A perennial, creeping plant. Soft leaf blades which are broad (up to 1cm wide) and blunt-tipped. Whorl Grass is found growing in or by shallow freshwater bodies.
Other Names:
Water WhirlGrass, Waterhair, Whorled Water-milfoil, Whorl-grass.
Frequency (UK):
Occasionally seen  

Other Information


Catabrosa aquatica, commonly known as Whorled water-milfoil, is a perennial aquatic plant that belongs to the grass family (Poaceae). It is native to the Northern Hemisphere and is common in the temperate regions of Europe, Asia and North America, found growing in freshwater habitats such as ponds, rivers, and lakes. The plant forms dense underwater stands in shallow water, growing up to 2-3 m long. The leaves are narrow, dark green and have a whorled or spiral arrangement. It produces small spikes of greenish-brown flowers which appear above the water surface in late summer.

The plant is considered a weed species because of its aggressive growth and ability to form large stands that can outcompete native aquatic plants, especially in areas with poor water quality. It also can clog water channels and boat propellers making it an invasive and problematic species in many aquatic habitats. In some places it is considered as a threatened species due to the pressure of urbanization and human-induced habitat destruction.


Whorl grass, also known by its scientific name Catabrosa aquatica, is a unique and fascinating aquatic plant that is found in wetlands, bogs, and other freshwater habitats throughout North America and Europe. This plant is known for its distinctive appearance, as it features a circular arrangement of leaves that grows around the base of its stem, hence its name "whorl" grass.

Catabrosa aquatica typically grows in shallow water, with its roots anchored in the muddy or sandy substrate at the bottom of the body of water. Its stems can reach up to 12 inches in height and are topped by the whorl of leaves that give the plant its distinct appearance. The leaves themselves are narrow and grass-like, typically about 2-4 inches long and 1-2 mm wide, and have a glossy green coloration.

One of the most interesting features of Catabrosa aquatica is its adaptation to its aquatic environment. This plant has evolved several unique characteristics that allow it to thrive in its watery habitat. For example, its leaves are covered in a waxy coating that helps to repel water, allowing the plant to remain buoyant and upright in the water. Additionally, its roots are adapted to absorb nutrients and oxygen from the surrounding water, which helps the plant to grow and thrive.

Despite its unusual appearance, Catabrosa aquatica plays an important role in the ecology of wetland and freshwater habitats. It provides habitat and shelter for a variety of aquatic animals, including fish, amphibians, and invertebrates. Additionally, it helps to filter and purify the water by removing excess nutrients and pollutants, which can improve water quality for other organisms in the ecosystem.

While Catabrosa aquatica is generally considered to be a harmless and beneficial plant, it can occasionally become invasive in some areas. Invasive populations of whorl grass can crowd out native plant species and disrupt the balance of the ecosystem, which can have negative impacts on local wildlife and water quality.

In addition to its ecological importance, Catabrosa aquatica also has some potential practical applications. For example, its waxy leaves could inspire the development of new waterproof coatings or materials, and its ability to absorb nutrients from the surrounding water could be used in bioremediation efforts to clean up polluted waterways.

However, due to its potential invasiveness, it is important to carefully monitor and manage populations of Catabrosa aquatica. In some areas, efforts may need to be taken to control its growth and prevent it from becoming a problem for native species and ecosystems.

Interestingly, Catabrosa aquatica has also been used in traditional medicine in some cultures. It has been used to treat a variety of ailments, including inflammation, gastrointestinal problems, and skin conditions. However, more research is needed to fully understand the medicinal properties of this plant and how it could be used in modern medicine.

Overall, Catabrosa aquatica is a fascinating and important plant that has a lot to offer in terms of ecology, practical applications, and traditional medicine. Its unique adaptations and distinctive appearance make it a valuable subject for further study and research. However, it is important to carefully manage its growth and prevent it from becoming invasive in areas where it is not native.

One interesting aspect of Catabrosa aquatica is its reproduction. Like many aquatic plants, it can reproduce both sexually and asexually. In sexual reproduction, the plant produces small flowers that are pollinated by wind or insects. The resulting seeds are then dispersed by water or animals, allowing the plant to spread to new areas.

In asexual reproduction, Catabrosa aquatica can produce new plants from its roots or stem fragments. This allows the plant to quickly colonize new areas and spread rapidly, which can be beneficial in some circumstances but can also contribute to its potential invasiveness.

In addition to its ecological and practical significance, Catabrosa aquatica is also a visually striking plant that can add beauty and interest to aquatic environments. Its circular whorls of leaves create a unique pattern that is both attractive and functional, helping the plant to capture sunlight and absorb nutrients from the surrounding water.

Overall, Catabrosa aquatica is a fascinating and important aquatic plant that has a lot to offer in terms of ecology, practical applications, and aesthetics. While it is important to manage its growth and prevent it from becoming invasive, this plant is a valuable and intriguing subject for further study and appreciation.

Distribution Map

Reproduced by kind permission of the BSBI.

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