Quick Facts

Quick facts

• Mexican Poppy (Argemone mexicana) is extremely poisonous, but instances of stock poising are rare due to it being unpalatable to stock.
• It is most common in Queensland, but has been recorded in Western Australia and New South Wales.
• It establishes readily on disturbed ground, especially where competition from other species is minimal.
• Mexican Poppy is commonly associated with dry river beds and sandy river flats.

What Does It Look Like?

What is it?

Mexican Poppy (Argemone mexicana) is an erect annual herb that grows to 1.5 m tall. The leaves are divided or lobed and bear small yellowish spines along the edges. The basal leaves form a rosette at ground level, but soon wither. The upper or stem leaves are 7-15 cm long and 2-6 cm wide, sometimes much larger and arranged alternately along the stems. They are bluish-green or greyish-green in colour, usually with whitish veins. The flowers are 3-7 cm in diameter and consist of six, bright yellow petals. Numerous bright yellow stamens and a purple stigma occur in the centre of the flowers. The fruits are spiny, oblong capsules 2.6-3.6 cm long and 1.4-1.8 cm wide and contain numerous small seeds 1.5-1.7 mm in diameter (Ownbey 2007).

The nomenclature of this species is somewhat complicated. It has sometimes been referred to in Australia as Argemone ochroleuca. Argemone ochroleuca is very similar in appearance and far more widespread than A. mexicana. To confuse matters further, both species are referred to as Mexican Poppy. Argemone mexicana differs from A. ochroleuca in having bright yellow flowers, as opposed to cream or pale-yellow flowers, as well as globular flower buds, as opposed to the egg-shaped buds of Argemone ochroleuca (Auld & Medd 1987).

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

Flower colour

Yellow

Growth form (weed type/habit)

Herb

Where it currently grows? Preferred habitat

Mexican Poppy grows in subtropical environments. It is a weed of many varied habitats, including roadsides, railway lines, waste areas, disturbed sites, degraded pastures, crops and fallow ground (Navie 2004; Ownbey 2007). It is often recorded as having an affinity for sandy river flats and ephemeral watercourses (Auld & Medd 1987; Parsons & Cuthbertson 2001).

Are there similar species?

The name Mexican Poppy is often also applied to another species of Argemone (Argemone ochroleuca). Argemone mexicana differs from A. ochroleuca by its bright yellow flowers and globular flower buds, as opposed to the pale yellow flowers and egg-shaped buds of A. ochroleuca. Argemone mexicana has a more tropical distribution in Australia (Auld & Medd 1987).

Another similar species that is also naturalised in Australia is the American Poppy (Argemone subfusiformis subsp. subfusiformis). This species is known to be naturalised only in north-eastern New South Wales. It has flowers that are generally larger than those of the Mexican Poppy and a less spiny capsule. When not flowering Mexican Poppy could be mistaken for a Thistle due to the presence of prickles on the stems and leaves (Ownbey 2007).

Why Is It A Weed?

What are its impacts?

Mexican Poppy grows well in sugarcane and cereal crops, but is generally not regarded as an aggressive crop weed in Australia. It establishes readily on wasteland and overgrazed pastures. The prickly fruits can become entangled in wool, reducing its value considerably. It is suspected of being toxic to animals and humans due to the presence of alkaloids in all parts of the plant. However, reported cases of poisoning are rare because livestock tend to avoid it in the field, due to the presence of a bitter sap that makes it unpalatable. Poisonings may occur as a result of hay and chaff containing traces of the plant. Poisonings in humans have occurred due to the consumption of oils contaminated with the plant (Parsons & Cuthbertson 2001). Mexican Poppy is a host for the Verticillium Wilt Fungus and the Tomato Spotted Wilt Virus (Bromilow 2001).

How does it spread?

Reproduction of Mexican Poppy occurs by seed. It is estimated that a single plant can produce up to 30 000 seeds per year. Seeds of Mexican Poppy usually fall close to the parent plant, but seed is also readily dispersed by moving water, especially where plants grow in riparian habitats and on terrain where erosion and runoff occurs. Contaminated soil, fodder, vehicles and the fur and hooves of livestock are also vectors for transport of Mexican Poppy seed (Parsons & Cuthbertson 2001).

What is its history in Australia?

It is unknown how and when Mexican Poppy was first introduced into Australia. It was first recorded from New South Wales in 1904, most likely as a cultivated specimen (National Herbarium of NSW 2007). It now occurs as a weed in south-east Queensland and north-eastern New South Wales and it has been recorded in Western Australia (Ownbey 2007).

How To Manage It?

Best practice management

As is the case with many annual weeds, control of Mexican Poppy should be aimed at the prevention of seed formation. Successful control of Mexican Poppy may be achieved by hand-pulling, grubbing or cutting plants before any fruits ripen. Seedlings can be controlled effectively with herbicide or by mowing. Good pasture management is effective in reducing the impact and preventing invasion of Mexican Poppy. Seedlings do not compete well with perennial crop and pasture species, nor does they compete well with established pasture (Parsons & Cuthbertson 2001).

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

Does it have a biological control agent?

NO

When does it grow? (lifecycle/growth calendar)

Mexican Poppy seeds germinate at any time of the year provided adequate moisture is available. Under normal seasonal conditions, young plants form a rosette during winter and produce flowering stems during spring. Flowering can occur throughout most of the year, but most often during spring and summer (Navie 2004). Mature seed remains dormant for up to three months after being shed from the parent plant (Parsons & Cuthbertson 2001).

Where Is It Found?

Which states and territories is it found?

NSW,  QLD, WA

What areas within states and territories is it found?

Mexican Poppy occurs in Western Australia, south-eastern Queensland and north-eastern New South Wales (Ownbey 2007). It is most common in Queensland where it has been recorded in the Moreton, North Kennedy, Port Curtis, Wide Bay, Leichhardt, Warrego and Darling Downs Regions (Queensland Herbarium 2007).

Where does it originate?

Mexican Poppy is native to North America (Florida and Mexico) and throughout South America (GRIN 2007).

National And State Weed Listings

Is it a Weed of National Significance (WONS)?

NO

Where is it a declared weed?

NSW, NT, 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

Argemone mexicana

Other scientific names (synonyms)?

Argemone mexicana L. var. mexicana

Does it have other known common name(s)?

Prickly Poppy