Mimosa (Mimosa pigra)

Also known as: giant sensitive tree, giant mimosa, thorny sensitive plant

Mimosa is a prickly shrub with pink flowers and fern-like leaves which fold closed at night or when touched. It forms dense thickets that outcompete native vegetation.

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How does this weed affect you?

Mimosa forms dense prickly thickets that can:

• invade grazing land, reducing productivity
• make mustering difficult and restrict livestock’s access to water
• outcompete native plants in grasslands, sedgelands and paperbark swamps
• reduce habitat for native animals, especially water birds and raptors
• invade wetlands
• impede Indigenous cultural activities such as hunting, fishing, collecting bush foods and access to sacred or cultural sites
• impact on recreational activities and tourism.

What does it look like?

Mimosa is a branched, prickly, perennial shrub that grows up to 6 m tall.

Leaves are:

• bright green
• 20–31 cm long
• arranged alternately along the stem
• divided into 6–16 pairs primary leaflets each about 5 cm long which are further divided into 20–45 pairs of secondary leaflets. The secondary leaflets are:
  • 3–12 mm long and 0.5–2.0 mm wide
  • stalkless and opposite
  • sensitive—they fold together at night or when they are touched.

 Leaves often have small curved prickles between the branchlets along the leaf stalk. There are also slender erect prickles between the pairs of primary leaflets.

Flowerheads are:

• pink-mauve 
• 1–2 cm wide
• shaped like a pom-pom containing up to 100 individual florets (tiny flowers)

Seed pods are:

• flattened usually 3–15 cm long and 0.7–1.4 cm wide
• olive green, turning brown as they age
• covered in fine, bristly hairs
• made up of 14–26 one-seeded segments, which break off as they age
• in groups of 1–30 pods per flower head.

Seeds are:

• light brown, brown or greenish-brown
• oblong
• 4–6 mm long and 2.0–2.5 mm wide.

Stems:

• are green when young turning woody with age
• have crved prickles (5–10 mm long)
• can form roots when they contact the ground.

Roots:

• a branching taproot 1–2 m deep
• woody at the base
• have nodules on the root hairs.

Similar looking plants

Mimosa is similar to common sensitive plant (Mimosa pudica) which is a creeping herb or low-growing shrub less than 1 m tall. It has smaller seed pods (1–2.5 cm long) which are made up of less (1–5) segments. It has been found occasionally in NSW.

Mimosa is not the same plant as mimosa bush (Vachellia farnesiana), which is widespread across NSW and common in the North West region of NSW. Mimosa bush has yellow, pom-pom shaped flowers and paired, straight thorns that are 5–25 mm long and only occur on the woody stems.

Where is it found?

Mimosa has not been recorded in NSW.

In Australia, mimosa is thought to have been introduced to the Darwin Botanic Gardens in the late 1800s. By the 1970s, mimosa spread into open floodplains and is now widespread in many river systems across the top end of the Northern Territory. In Queensland, mimosa has only been found at a dam near Proserpine and is currently targeted for eradication.

Mimosa is a native of tropical, Central and South America. It has become a serious weed in parts of Africa, Asia, North America and Oceania.

What type of environment does it grow in?

Mimosa grows best in moist, humid areas in the tropics and sub-tropics. It prefers a wet-dry tropical climate with rainfall above 750 mm per year. In lower rainfall regions it usually only grows in wetlands and near watercourses. It grows on a wide variety of soil types and tolerates flooding.

Floodplains, riverbanks and seasonal wetlands are ideal environments for mimosa. Disturbed sites such as roadsides, drainage ditches, around dams and grazing land are also suitable.

Maps and records

• Recorded presence of Mimosa during property inspections (Map: Biosecurity Information System - Weeds, 2017-2023)
  These records are made by authorised officers during property inspections under the Biosecurity Act 2015. Officers record the presence of priority weeds in their council area and provide this to the NSW Department of Primary Industries. Records reflect the presence of the weed on the date of inspection.
  
  

How does it spread?

By seed

Mimosa plants can flower within one year of germination. Large mimosa trees produce up to 220,000 seeds per year. In northern Australia, mimosa seed banks can reach up to 12,000 seeds per square metre. Mimosa seed may remain viable for over 10 years. Seeds generally germinate in high numbers when exposed to moisture. Plants tend to live for a maximum of 5 years.

 Mimosa seeds spread:

• by floating in waterways, especially during floods (most common way)
• when the bristly hairs on the seed pods attach to fur, hair, clothes or shoes
• by passing through animals such as cattle and horses that eat the seed pods
• in contaminated mud stuck to vehicles, boats or machinery.

By plant parts

Mimosa could also spread via stem fragments, although seed is thought to be the primary means of spread.

References

CRC for Australian Weed Management (2003). Weed Management Guide: Mimosa.

Lloyd, S.G. & Vinnicombe, T.L. (2010). Mimosa pigra L. - a new incursion into Western Australia In Proceedings of the 17th Australasian Weeds Conference. pp180-181.

Parsons, W.T. & Cuthbertson, E.G. (2001). Noxious weeds of Australia, CSIRO Publishing, Collingwood.

Queensland, Department of Agriculture and Fisheries (2020). Restricted Plant: Mimosa. Retrieved October 2020 from: https://www.daf.qld.gov.au/__data/assets/pdf_file/0007/65149/mimosa-pigra.pdf

More information

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Control

Please do not attempt to treat or dispose of this weed yourself. Report this plant if you see it anywhere in NSW by calling the helpline listed at the top of this page immediately.

NSW DPI will lead an initial response for the treatment and disposal of the plant to stop it from spreading.

Herbicide options

See Using herbicides for more information.

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PERMIT 9907 Expires 31/03/2025
Fluroxypyr 200 g/L (Comet® 200 herbicide)
Rate: 35 mL per L diesel/kerosene
Comments: Basal bark
Withholding period: Do not graze failed crops and treated pastures or cut for stock feed for 7 days after application. See label for further information.
Herbicide group: I, Disruptors of plant cell growth (synthetic auxins)
Resistance risk: Moderate

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PERMIT 9907 Expires 31/03/2025
Fluroxypyr 333 g/L (Starane™ Advanced)
Rate: 21 mL per L diesel/kerosene
Comments: Basal bark
Withholding period: Do not graze failed crops and treated pastures or cut for stock food for 7 days after application. See label for more information.
Herbicide group: I, Disruptors of plant cell growth (synthetic auxins)
Resistance risk: Moderate

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PERMIT 9907 Expires 31/03/2025
Glyphosate 360 g/L (Various products)
Rate: One part product to 1.5 parts water
Comments: Cut stump, drill, frill axe or injection.
Withholding period: Nil.
Herbicide group: M, Inhibitors of EPSP synthase
Resistance risk: Moderate

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PERMIT 9907 Expires 31/03/2025
Glyphosate 360 g/L with Metsulfuron-methyl 600 g/kg (Various products)
Rate: 1:1.5 glyphosate to water + 1 g metsulfuron to 1 L water
Comments: Stem injection
Withholding period: Nil.
Herbicide group: M, Inhibitors of EPSP synthase
Resistance risk: Moderate

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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 pest 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.
All of NSW	Prohibited Matter A person who deals with prohibited matter or a carrier of prohibited matter is guilty of an offence. A person who becomes aware of or suspects the presence of prohibited matter must immediately notify the Department of Primary Industries

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Reviewed 2020