Weed Alert: Yellow burrhead

Yellow burrhead (limnocharis flava)

World Status | Identification | Growth and Spread  | Legislation

Yellow burrhead is an aquatic plant that has the potential to become a major weed of wetlands, slow moving streams and dams in semi-tropical and tropical areas of Australia.

It colonises shallow wetlands and the margins of deeper waterways where it can quickly grow to dominate other aquatic plants. The leaves and stems slow water movement in channels and drains causing silt to built up, eventually blocking water flow.

With unusual foliage and attractive flowers, yellow burrhead is likely to be lurking unrecognised in suburban backyards, especially those featuring ‘Asian water gardens’.

This plant is banned from entry into Australia.

World Status

Yellow burrhead is a native of Central America (from Mexico through to Paraguay) and the Caribbean Islands. It has naturalised in the USA, Sri Lanka, India and south-east Asia including Indonesia, where it is threatening wetlands and has become a problematic weed of rice fields and irrigation channels.

In Asia it has been used as a food source but severe infestations have forced farmers to abandon rice paddies.

Several small naturalised populations and individual plants in garden ponds were discovered in the Cairns and Townsville districts in 2001-2002. A nationally funded eradication campaign is currently underway to remove isolated populations of yellow burrhead in northern Queensland.

Identification

Yellow burrhead is a perennial herb that prefers shallow, still water where it roots in mud. It emerges from the water and grows to 1 m high.

Leaves and stems

Triangular fleshly leaf stalks and flowering stems grow in clumps from seed or daughter plants. The leaf stalks are 5–75 cm long and green. The leaves above the leaf stalk are broad and oval shaped (5–30 cm long and 4–25 cm wide).

Flowers

The small, yellow, three-‘petalled’ flowers grow in clusters of up to 15 at the end of a stalk. Plants flower all year round.

Fruit and seeds

Each fruit is 2 cm wide and made up of many crescent-shaped segments. A single fruit can produce about 1000 seeds. The seeds are dark brown, horseshoe-shaped, about 1.5 mm long with obvious ridges.

Growth and Spread

Yellow burrhead reproduces both by seed and vegetatively. It behaves as a perennial in areas that have year-round wet conditions and as an annual in areas that endure dry seasons. It thrives in nutrient-enriched water and multiplies rapidly.

This prolific seed producing plant is capable of producing 1 million seeds per year. After fruiting, the flower stalk bends towards the water and releases the fruit onto the surface. The fruit eventually split into segments that float to new locations and these segments then break down to release seeds.

Plantlets develop after a flowering stem looses all of its flowers and bends over into the mud. The end of the stem then takes root in the mud below or breaks off and floats away to form new infestations.

Legislation

Limnocharis flava is a Class 1 noxious weed throughout NSW under the NSW Noxious Weeds Act 1993. This weed must be eradicated from the land and the land must be kept free of the plant.  As a notifiable weed, all outbreaks must be reported to the local council within three days.

Acknowledgements

Prepared by Annie Johnson and Rachele Osmond