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types of weed called burr weed tall stem black seeds

burr medic

Burr medic (Medicago polymorpha) has hairless (i.e. glabrous) stems and leaves. Its flowers are borne in small clusters, each containing 2-10 flowers. The coiled fruit (4-11 mm across) are covered in slender spines, or they are occasionally spineless and have a bumpy (i.e. tuberculate) surface.

Widely naturalised throughout most of the country, but most common in southern and eastern Australia. Common in southern and central Queensland, New South Wales, the ACT, Victoria, Tasmania, southern South Australia and south-western Western Australia.

A common weed of crops, pastures, riparian vegetation, revegetation areas, roadsides, disturbed istes, waste areas, parks, footpaths, gardens, lawns and other turfed areas.

A short-lived (i.e. annual) herbaceous plant with creeping (i.e. prostrate) or spreading (i.e. decumbent) stems.

Burr medic (Medicago polymorpha) is regarded as an environmental weed in Victoria, New South Wales and Western Australia.

"The slender green stems are practically hairless (i.e. sub-glabrous).

The alternately arranged leaves are once-compound with three leaflets (i.e. trifoliate) and are borne on stalks (i.e. petioles) about 30 mm long. The leaflets (5-25 mm long and 3-23 mm wide) are egg-shaped in outline (i.e. obovate) or almost heart-shaped (i.e. cordate). They are almost hairless (i.e. glabrate) and have slightly toothed (i.e. dentate) margins."

"The small pea-shaped flowers (3-6 mm long) are arranged in small clusters (2-10) in the upper leaf forks (i.e. axils). Each of these yellow flowers are borne on short stalks (i.e. pedicels). Flowering occurs from late winter through to early summer.

The fruit are coiled pods (4-10 mm across) and they are usually adorned with many slender spines or prickles (2-3 mm long). However, the spines may be reduced to small bumps in some forms of this species. Each pod contains several, brown, kidney-shaped (i.e. reniform), seeds."

"Burr medic (Medicago polymorpha) may be easily confused with cut-leaved medic (Medicago lacinata), woolly burr medic (Medicago minima), barrel medic (Medicago truncatula), spotted medic (Medicago arabica), black medic (Medicago lupulina) and yellow suckling clover (Trifolium dubium ). These species can be distinguished by the following differences:

Yellow burr weed: declared pest

Please note: This content may be out of date and is currently under review.

Yellow burr weed ( Amsinckia species) is a declared pest in Western Australia (WA). This article describes the nature of the plant with links to requirements land owners/occupiers must adhere to and pest control methods.

Yellow burr weed Amsinckia intermedia_DAFWA.jpg

Form: herbaceous — annual

Status: present in WA

Yellow burr weed (Amsinckia spp.) is native to North and South America. Yellow burr weed grows vigorously on a wide range of soil types, including sandy surfaced mallee soils, black clays and red loams. The three species of Amsinckia are declared plants throughout WA. Their features are similar so for practical purposes they can be treated as one weed.


Yellow burr weed is an erect herb reproducing only from seeds. It germinates over an extended period in the autumn and winter, making it very difficult to control by cultivation.

Stems: Bristly erect stems up to 70 centimetres high.

Leaves: Dark green to grey-green true leaves, with fleshy prominent midribs and rough surfaces. The rosette leaves are oval up to 15 centimetres long by four centimetres wide while the leaves of the flowering stems are narrower. Leaves are sessile (stalkless) and arranged alternately on the stem. All leaves are covered with short stiff hairs and feel rough to the touch. It has Y-shaped cotyledons (seed leaves).

Flowers: The small flowers are yellow to orange, and numerous. They are formed on one side of a 10-15 centimetres curved spike at the ends of the branches.

Seeds: Four hard rough angular seeds about 2.5 millimetres long, surrounded by a husk covered with stiff bristles are formed on each flower. The seeds fall to the ground when ripe.

Agriculture and economic impact

Yellow burr weed is a major weed of cereals in northwest United States, the Wimmera and Mallee districts of Victoria and in New South Wales. Isolated infestations have been found occasionally in the cereal growing areas of WA.

Yellow burr weed competes vigorously with cereals for light and nutrients, mainly nitrogen, having a serious impact on yields.

The plant contains poisonous alkaloids which cause liver damage. Pigs, cattle and horses have been poisoned by eating contaminated seed; however, sheep and poultry are relatively resistant.

Declared pest category

The Western Australian Organism List (WAOL) contains information on the area(s) in which this pest is declared and the control and keeping categories to which it has been assigned in Western Australia (WA). Search for yellow burr weed in the WAOL the scientific name Amsinckia

Requirements for land owners/occupiers and other persons

Requirements for land owners/occupiers and other persons if this pest is found can be sourced through the declared plant requirements link.

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MyPestGuide™ Reporter
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Pest and Disease Information Service (PaDIS)
+61 (0)8 9368 3080
[email protected]

Control method

Yellow burr weed is resistant to control by the phenoxy (hormone) herbicides. Control methods for this declared plant can be found through the yellow burr weed control link.