East Indian hygrophila (Hygrophila polysperma)

Also known as: polysperma, Indian swamp weed

Profile

Impact

East Indian hygrophila is a plant that has the potential to become a serious weed of freshwater lakes, ponds and dams in northern coastal New South Wales (NSW). This fast growing and fast spreading plant shades and out competes other submerged plants.

A related species Hygrophila (H. costata) is a declared noxious weed throughout North Eastern NSW.

Distribution

East Indian hygrophila is mostly found in tropical regions of the world and is native to South East Asia (Sri Lanka and India through to Vietnam). It is a significant aquatic weed in the warm areas of the United States where it was introduced by the aquarium trade.

East Indian hygrophila has been found in the Caboolture river in South Eastern Queensland and in the Tweed river on the North Coast of NSW.

Spread

East Indian hygrophila can grow in water up to 3 metres deep. It is adapted to low light conditions and expands rapidly where it can spread up to 4 hectares a year. It tends to grow more vigorously in flowing water.

The main method of reproduction is vegetative. The stems fragment easily and develop into new plants. Fragments can be transported by boats, fishing gear or just drift in the water to new locations. The importance of seeds in reproduction is not certain.

Description

East Indian hygrophila is mostly a submerged plant but will grow above water as an emerged plant in shallow water. It is a perennial herb, 50 (rarely to 100) cm high. The emerged shoots form dense floating mats.

Stems

Creeping stems grow both above and below the water. Emergent stems are squarish in cross-section and slightly hairy. Submerged stems are round and can grow over 2 metres long. The stems easily form new roots at each node.

Leaves

The leaves can be bright green to brown or reddish. They are 0.7-8 cm long elliptic in shape and with pointy tips. Leaves are covered in fine white hairs and grow in opposite pairs on the stem. Submerged leaves are longer with small leaf stalks; emerged leaves have no leaf stalk and are slightly rounder.

East Indian hygrophila (Hygrophila polysperma) can be distinguished from hygrophila (Hygrophila costata) which has leaves up to 18 cm long.

Flowers

The flowers grow out between the leaf and the stem of the upper leaves. They are a bluish-white and 5-6 mm long. Half the length of the flower is a tube.

Fruit

The narrow fruit capsule is 6-7 mm long and splits lengthwise to release 15-25 seeds. Seeds are pale brown, round and flattened, about 0.8 mm in diameter.

Habitat

It is found in warmer climates and prefers flowing water but may also be found in slow moving waters and lakes.

Acknowledgements

Prepared by Annie Johnson, NSW DPI, Orange.

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Control

East Indian hygrophila is difficult to control due to its stem fragmentation. Small infestations may be removed by hand. But it can quickly reinfest an area if fragments are left behind. Contact your local council weed officer for advice.

Herbicide options

Contact your local council weeds officer for control advice for East Indian hygrophila (Hygrophila polysperma).

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Legal requirements

The content provided here is for information purposes only and is taken from the Noxious Weeds Act 1993.

Area Class Legal requirements
Bellingen 3 Regionally Controlled Weed
The plant must be fully and continuously suppressed and destroyed and the plant must not be sold, propagated or knowingly distributed
Central Coast 3 Regionally Controlled Weed
The plant must be fully and continuously suppressed and destroyed and the plant must not be sold, propagated or knowingly distributed
Cessnock 3 Regionally Controlled Weed
The plant must be fully and continuously suppressed and destroyed and the plant must not be sold, propagated or knowingly distributed
Clarence Valley 3 Regionally Controlled Weed
The plant must be fully and continuously suppressed and destroyed and the plant must not be sold, propagated or knowingly distributed
Coffs Harbour 3 Regionally Controlled Weed
The plant must be fully and continuously suppressed and destroyed and the plant must not be sold, propagated or knowingly distributed
Dungog 3 Regionally Controlled Weed
The plant must be fully and continuously suppressed and destroyed and the plant must not be sold, propagated or knowingly distributed
Kempsey 3 Regionally Controlled Weed
The plant must be fully and continuously suppressed and destroyed and the plant must not be sold, propagated or knowingly distributed
Lake Macquarie 3 Regionally Controlled Weed
The plant must be fully and continuously suppressed and destroyed and the plant must not be sold, propagated or knowingly distributed
Maitland 3 Regionally Controlled Weed
The plant must be fully and continuously suppressed and destroyed and the plant must not be sold, propagated or knowingly distributed
Mid-Coast 3 Regionally Controlled Weed
The plant must be fully and continuously suppressed and destroyed and the plant must not be sold, propagated or knowingly distributed
Nambucca 3 Regionally Controlled Weed
The plant must be fully and continuously suppressed and destroyed and the plant must not be sold, propagated or knowingly distributed
Newcastle 3 Regionally Controlled Weed
The plant must be fully and continuously suppressed and destroyed and the plant must not be sold, propagated or knowingly distributed
Port Macquarie-Hastings 3 Regionally Controlled Weed
The plant must be fully and continuously suppressed and destroyed and the plant must not be sold, propagated or knowingly distributed
Port Stephens 3 Regionally Controlled Weed
The plant must be fully and continuously suppressed and destroyed and the plant must not be sold, propagated or knowingly distributed
Rous County Council 4 Locally Controlled Weed
The growth of the plant must be managed in a manner that continuously inhibits the ability of the plant to spread and the plant must not be sold, propagated or knowingly distributed
Upper Hunter County Council 3 Regionally Controlled Weed
The plant must be fully and continuously suppressed and destroyed and the plant must not be sold, propagated or knowingly distributed

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For technical advice and assistance with identification please contact your local council weeds officer.
For further information call the NSW Invasive Plants and Animals Enquiry Line on 1800 680 244 or send an email to weeds@dpi.nsw.gov.au

Reviewed 2014