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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Biosecurity duty

The content provided here is for information purposes only and is taken from the Biosecurity Act 2015 and its subordinate legislation, and the Regional Strategic Weed Management Plans (published by each Local Land Services region in NSW). It describes the state and regional priorities for weeds in New South Wales, Australia.

Area Duty
All of NSW General Biosecurity Duty
All plants are regulated with a general biosecurity duty to prevent, eliminate or minimise any biosecurity risk they may pose. Any person who deals with any plant, who knows (or ought to know) of any biosecurity risk, has a duty to ensure the risk is prevented, eliminated or minimised, so far as is reasonably practicable.
Central West Regional Recommended Measure*
Land managers should mitigate the risk of new weeds being introduced to their land. The plant should be eradicated from the land and the land kept free of the plant. The plant should not be bought, sold, grown, carried or released into the environment. Notify local control authority if found.
Greater Sydney Regional Recommended Measure*
Land managers should mitigate the risk of new weeds being introduced to their land. The plant should be eradicated from the land and the land kept free of the plant. The plant should not be bought, sold, grown, carried or released into the environment. Notify local control authority if found.
Hunter Regional Recommended Measure*
Land managers should mitigate the risk of new weeds being introduced to their land. The plant should be eradicated from the land and the land kept free of the plant. The plant should not be bought, sold, grown, carried or released into the environment. Notify local control authority if found.
North Coast
Exclusion zone: all waters in the region excluding the core infestation area of Richmond Valley Council, Ballina Shire Council, Lismore Council, Kyogle Council, Byron Shire Council and Tweed Shire Council.
Regional Recommended Measure*
Whole region: The plant or parts of the plant should not be traded, carried, grown or released into the environment. Exclusion zone: The plant should be eradicated from the land and the land kept free of the plant. Land managers should mitigate the risk of the plant being introduced to their land. Core infestation area: Land managers should reduce impacts from the plant on priority assets.
North West Regional Recommended Measure*
Land managers should mitigate the risk of new weeds being introduced to their land. The plant should be eradicated from the land and the land kept free of the plant. The plant should not be bought, sold, grown, carried or released into the environment. Notify local control authority if found.
*To see the Regional Strategic Weeds Management Plans containing demonstrated outcomes that fulfill the general biosecurity duty for this weed click here

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Reviewed 2017