Quick Facts

Quick facts

• Originally from North, Central and South America, Hygrophila (Hygrophila costata) is an aquatic herb growing to 90 cm high.
• It can be found growing in waterways, lakes, dams and ponds.
• Hygrophila was almost certainly introduced into Australia as an aquarium plant, and has since spread into natural habitats from disposal of aquarium contents into waterways.
• This species grows aggressively and forms dense mats that can displace and out-compete native plant species in shallow water and adjacent damp soils.
• It produces abundant tiny seeds that adhere readily to wildlife and water craft.

What Does It Look Like?

What is it?

Hygrophila (Hygrophila costata) is an aquatic herb growing to 90 cm high. The stems are four-sided, grooved lengthways and are hairless or moderately to densely hairy. The oval-shaped leaves have very short stalks, tips that end in a short point, and are up to 90 mm long and 20 mm wide. They can be somewhat hairless or sparsely hairy on the upper and lower surfaces, particularly on the veins.

The flower heads comprise clusters of 10 or more flowers on very short stalks. The outer 'flowers' have five lobes, and are 5.5–6 mm long, with short hairs on the edges and middle vein. The white flowers are tubular, 3.5 mm long, and are comprised of a 2.5 mm long, two lobed upper lip and a 3 mm long, three lobed lower lip.

The fruit is a narrowly oval shaped capsule, 6-8 mm long, containing about 20 seeds that are more numerous at the base of the capsule (Barker 2008 pers. comm.).

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

Flower colour

White

Growth form (weed type/habit)

Herb, Aquatic

Where it currently grows? Preferred habitat

Hygrophila occurs in waterways, lakes, dams, ponds and wetlands predominantly in subtropical, tropical and warm temperate areas (Navie 2004).

Are there similar species?

Hygrophila can be confused with the native species Hygrophila angustifolia but the latter species is a smaller plant (15-45 cm compared to up to 90 cm) with very narrow leaves (2-8 mm wide compared to 20 mm), and relatively large fruit (10-18 mm long compared to 6-8 mm) (Navie 2004; Barker 2008 pers. comm.).

Hygrophila is also similar to Senegal Tea Plant (Gymnocoronis spilanthoides) but the latter species has somewhat hollow stems and leaves with finely-toothed edges. These traits are not present in Hygrophila (Navie 2004).

Dyschoriste depressa has only relatively recently been recognised from the Brisbane area. It occupies similar habitat to Hygrophila and could be easily confused with it since it has the same clusters of flowers and fruits in the axils. However, Dyschoriste depressa has distinct bristles at the base of each of the male reproductive parts of the flower and fruit which contain only four seeds (Barker 2008 pers. comm.).

Why Is It A Weed?

What are its impacts?

Native ecosystems: Hygrophila is a serious weed of waterways in coastal New South Wales and south-eastern Queensland. It grows aggressively, forming dense mats which can displace and out-compete most other native species in shallow water and adjacent damp soils (Thorp & Wilson 1998). It also disrupts habitat for local fauna (Gorham & Hosking 2003).

How does it spread?

Hygrophila has almost certainly been introduced as an aquarium plant and become naturalised from disposal of aquarium contents into local rivers (Barker 2008 pers. comm.). The sticky seeds can adhere to animals, machinery, and water craft and plants can spread locally via rooting nodes (Thorp & Wilson 1998; Gorham & Hosking 2003).

What is its history in Australia?

Hygrophila was almost certainly introduced into Australia as an aquarium plant (Barker 2008 pers. comm.). It has only been collected in Australia since the 1990s suggesting that this species is a recent naturalisation (Gorham & Hosking 2003).

How To Manage It?

Best practice management

Control of Hygrophila is very difficult as new infestations can form from any remaining pieces of the plant (NSW DPI, 2020). Correct disposal of plant parts is important for limiting spread; all plants should be carefully handled and bagged (Pritchard 2004).

Chemical control: Some herbicides are effective, but care must be taken when using herbicides near waterways (Pritchard 2004).

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

Non-chemical control: Physical control: Hand removal of isolated plants is beneficial, but large scale hand removal of larger infestations may cause damage to native vegetation or aquatic ecosystems. Planting large shading trees can reduce the growth of Hygrophila by shading and competition. Preventing animal or mechanical access to infested areas should reduce the spread of seed or other plant parts (Pritchard 2004).

Does it have a biological control agent?

NO

When does it grow? (lifecycle/growth calendar)

Hygrophila flowers from October to March (Barker 2008 pers. comm.). It is not known how long seeds remain viable (Pritchard 2004). In North America, dense stands of shoots are produced with elongated nodes (joints in the stem) and large leaves which will extend upward to the water surface from depths exceeding 3 m. Emergent shoots have smaller, more compact, darker green leaves and shorter internodes (area between nodes). When rooted on moist banks the shoots are only 15-20cm tall. If submerged, the emergent shoots will drop their leaves and produce new leaves of the underwater type. Elongation of shoots begins with the increase in water temperature in early spring. Shoots reach the surface in late spring. During the summer, fragments with numerous adventitious roots break away from the mats. Upon contact with soil they will readily root. During the hot weather of late summer the whole shoot will break off near the root crown. These shoots form large, heavy, floating mats, which can cause severe water flow problems. The whole mat can sink and produce a new colony, or individual pieces can do so. The old root crowns quickly produce new shoots, which grow slowly during the winter (Hall & Vandiver 1990).

Where Is It Found?

Which states and territories is it found?

NSW, QLD

What areas within states and territories is it found?

Hygrophila has naturalised in south-eastern Queensland and north-eastern New South Wales. It has been recorded in recent years from swampy margins of Lake McDonald in Queensland where it has formed a weedy thicket (Barker 2008 pers. comm.). In New South Wales, it has naturalised in wetland areas near Casino, along Byron Creek near Bangalow, and Burringbar Creek at Mooball (Gorham & Hosking 2003).

Where does it originate?

Hygrophila is native to North, Central and South America (Navie 2004).

National And State Weed Listings

Is it a Weed of National Significance (WONS)?

NO

Where is it a declared weed?

NSW, QLD, 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 costata

Other scientific names (synonyms)?

Hygrophila "Lake McDonald" (Bean 6770)

Does it have other known common name(s)?

Lake Hygrophila, Glush Weed, Gulf Swampweed, Temple Weed, Sword Leaf Stricta