Quick Facts

Quick facts

• Originally from the Indian Sub-continent and south-east Asia, Indian Swampweed (Hygrophila polysperma) was introduced to Australia through the aquarium trade.
• Indian Swampweed probably found its way into river systems by the discarding of aquarium contents.
• It is an aggressive weedy species which quickly spreads in aquatic environments.
• It readily reproduces by stem fragmentation, and almost certainly by the copious production of tiny seeds, making it difficult to control.
• It can form dense mats which shade out other submerged plants and restrict water flow.

What Does It Look Like?

What is it?

Indian Swampweed (Hygrophila polysperma) is a low-growing creeping herb that may grow up to 20 cm high on dry land. The stems are white in the younger parts, becoming reddish and leafless at the base, rounded in cross section and hairless in the vegetative parts, but quadrangular in cross section and hairy in the flowering shoots. Roots may form from all of the lower nodes (points where leaves, or roots, arise) of the stem. The leaves are stalkless (sessile), oval (elliptic) to egg-shaped (ovate), 5–20 mm long and 3-5 mm wide, with entire leaf margins i.e. without teeth or lobes, and with the midrib (midvein) raised on the lower surface.

The pale mauve to blue flowers are sessile, and form spike-like clusters in the axils (angles) of the upper bracts (modified apical leaves); flowers have only been observed on plants which are not in the water (Virginia Seymour, Far North Coast City Council, pers. comm.). The bracts are leaf-like and densely hairy on both surfaces. The corolla (collective term for petals) is 4.5–5 mm long, tubular for most of its length and externally hairless. The flower tubes are made up of an entire (unlobed) upper lip, and a three lobed lower lip that may be turned down at right angles to the tube, with the central lobe wider than the two side lobes.

The fruit is a 4.5–5.5 mm long capsule with a hairy tip; it contains 24–30 seeds, each of them covered with hairs that expand on wetting (Barker 2008 pers. comm.).

For further information and assistance with identification of Indian Swampweed, contact the herbarium in your state or territory.

Flower colour

Blue, Purple

Growth form (weed type/habit)

Herb, Aquatic

Where it currently grows? Preferred habitat

In Australia, Indian Swampweed is a potential weed of freshwater lakes, dams and ponds. It prefers warmer climates and is usually found in flowing water, but does occur in slower flowing waterways and lakes (Johnson 2003). It can grow in water up to 3 m deep, and is adapted to low-light conditions and tolerant of a wide pH range (Johnson 2003; Robinson 2003).

Are there similar species?

Indian Swampweed can be confused with the native species Hygrophila angustifolia, but the native species does not grow in submerged situations. H. angustifolia also has well-developed hooks under each of the seeds in the capsule, whereas Indian Swampweed does not have these hooks. H. angustifolia also has 4 stamens (male organs that include the pollen bearing anthers) to a flower rather than 2 for Indian Swampweed (Barker 2008 pers. comm.).

The weedy Hygrophila species (H. costata), also known as Glush Weed (Thorp & Wilson 1998 – ), is more prevalent in Australia, and is found in similar habitats to Indian Swampweed. The flowers of Hygrophila are white, 3.5 mm long and have a two lobed upper lip, while the flowers of Indian Swampweed are pale mauve to blue, 4.5-5 mm long, and have an unlobed upper lip (Barker 2008 pers. comm.).

Dyschoriste depressa has only relatively recently been recognised as now occurring in the Brisbane area. It occupies similar habitat to Indian Swampweed and could be easily confused with it since it has the same clusters of flowers and fruits in the axils (angles between the stem and leaf). However, it may be distinguished from Indian Swampweed by its distinct awn (sharp protuberance) at the base of each of the anthers (pollen bearing parts of the stamen) or the capsules that contain only 4 seeds compared with many more seeds in Indian Swampweed (Barker 2008 pers. comm.). Further information and images of Dyschoriste depressa can be found on the Weed Society of Queensland site (2006).

Why Is It A Weed?

What are its impacts?

Indian Swampweed is an aggressive, fast-growing weed that, once established, forms dense mats which can out-compete other submerged plants, including strongly competing for light and shading out other species (Johnson 2003). These mats can also obstruct water flow, impair water quality, and impede navigation of waterways (Robinson 2003).

Native ecosystems: The dense stands of Indian Swampweed often change the habitat suitability for native fauna, ultimately resulting in ecosystem disruption and a loss of biodiversity (Robinson 2003). When these large stands die, their decomposition can create toxic, low oxygen conditions which may result in the death of fish species (Robinson 2003).

How does it spread?

Indian Swampweed is introduced into waterways by the discarding of aquarium contents (Barker 2008 pers. comm.). Plant fragments may be spread by attaching to animals, machinery, water craft and fishing gear, or may float freely along waterways. Seed dispersal may occur, but its relative importance in the spread of this weed is uncertain (Johnson 2003).

What is its history in Australia?

Indian Swampweed was almost certainly introduced into Australia as an aquarium plant and has become naturalised through the discarding of aquarium contents into waterways. It is a relatively recent introduction to Australia with the first confirmed records being made in 2005 (Barker 2008 pers. comm.).

How To Manage It?

Best practice management

Indian Swampweed can be difficult to control as it readily reproduces from small stem fragments.

Chemical control: Indian Swampweed is difficult to control with herbicides and greater volumes or chemicals are needed compared to other water weeds (Johnson 2003; Robinson 2003).

Please see the Australian Pesticides and Veterinary Medicines Authority for chemical information http://www.apvma.gov.au 

Non-chemical control: Physical control: Small infestations can be removed by hand, but care must be taken to remove all plant fragments. Larger infestations are more difficult to control. Mechanical control: These may be mechanically harvested, but this tends to create fragments which can be transported by boats or wildlife, or flow downstream and create new populations.

Does it have a biological control agent?

NO

When does it grow? (lifecycle/growth calendar)

Indian Swampweed flowers around June in New South Wales. It does not appear to produce flowers when submerged (Barker 2008 pers. comm.). It flowers in autumn in the United States of America (Robinson 2003).

Where Is It Found?

Which states and territories is it found?

NSW, QLD

What areas within states and territories is it found?

Indian Swampweed was first collected in Australia in August 2005 in the Caboolture River north of Brisbane (Weeds of Australia, 2020), and in the Tweed River in New South Wales (Johnson 2003). It is likely that there are also populations in the Orara, Clarence and Wilson Rivers of the Far North Coast region of New South Wales (Stephen Johnson, NSW DPI, pers. comm.). Other collections have been made near Babinda in Far North Queensland.

Where does it originate?

Indian Swampweed is native to south-eastern Asia: Sri Lanka, India, through to Vietnam (Johnson 2003).

National And State Weed Listings

Is it a Weed of National Significance (WONS)?

NO

Where is it a declared weed?

NSW, WA

Government weed strategies and lists – Weeds Australia

Is it on the National Alert List for Environmental Weeds?

NO

Government weed strategies and lists – Weeds Australia

Is it on the Agricultural Sleeper List?

NO

Government weed strategies and lists – Weeds Australia

Names And Taxonomy

Main scientific name

Hygrophila polysperma

Other scientific names (synonyms)?

• Hemiadelphis polysperma (Roxb.) Nees.
• Justica polysperma Roxb.

Does it have other known common name(s)?

Indian Swamp Weed, East Indian Hygrophila, Eastern Indian Hygrophila, Miramar Weed