Stemless thistle

Common name:

  • Stemless thistle

Scientific name:

  • Onopordum acaulon L.

Plant status

Catchment management authority boundaries

Stemless thistle catchment map

Regionally prohibited in the Port Phillip and Western Port catchments.

Regionally controlled in the East Gippsland and North East catchments.

Restricted in the Mallee, West Gippsland, North Central Glenelg Hopkins, Corangamite, Wimmera and Goulburn Broken catchments.

Plant biology

Appearance

Herbaceous plant  — Forb (flowering herbaceous plant  — not a grass)

Description

Stemless thistle is a prostrate annual or biennial herb.Whole plant of stemless thistle

Stems

Absent.

Leaves

Leaves of stemless thistle are whitish and very woolly, growing to 40cm long. Leaf lobes are deep and undulate and leaves have many spines on the margins. Leaves have short stalks and are arranged in a large rosette.

Flowers

The flowers of stemless thistle are white to purple florets with globular heads. They are sessile (without stalks), grow to 6cm in diameter and are clustered in the centre of the rosette with each head surrounded by numerous sharply spined bracts.Stemless thistle infestation

Fruit

No fruit.

Seeds

Seeds of stemless thistle are brown or grey, 4 to 5mm long, quadrangular, pitted and ridged lengthwise. It has a pappus of cream-coloured barbed hairs 2 to 2.5cm long.

Growth and lifecycle

Method of reproduction and dispersal

With a large feathery pappus, the seeds of the stemless thistle are well adapted for wind dispersal. In Victoria, aided by prevailing winds, seeds have been dispersed over 200m.

Dispersal also occurs when seeds contaminate agricultural produce, vehicles and animals. However, this dispersal method is of minor importance compared with wind dispersal.

Seed is also spread via birds in:

  • hay
  • silage
  • chaff
  • commercial seed
  • water.

Seedbank propagule persistence

Stemless thistle can reproduce as either an annual or biennial. It produces 8 flower heads per plant with 150 seeds per head resulting in 1200 seeds per plant.

Stemless thistle seed can survive in the soil for several years making eradication difficult. Plants cut below the surface with cultivation equipment may re-sprout from root fragments, commonly producing multiple crowns.

Preferred habitat

Stemless thistle prefers warm-temperate regions typically in areas receiving less than 450mm of annual rainfall  — more prevalent on sandy soils but also occasionally appears on heavier calcareous soils. It is drought tolerant and found mainly in pastures, roadsides and neglected areas.

Distribution

Stemless thistle invades Mallee shrubland, lowland grassland and grassy woodland.

Growth calendar

The icons on the following table represent the times of year for flowering, seeding, germination, the dormancy period of stemless thistle and also the optimum time for treatment. th> Dormancy

 JanFebMarAprMayJunJulAugSepOctNovDec
Flowering         Flowering iconFlowering icon 
SeedingSeeding icon         Seeding iconSeeding icon
Germination  Germination iconGermination iconGermination iconGermination iconGermination iconGermination icon    
Dormancy            
Treatment     Treatment iconTreatment iconTreatment iconTreatment iconTreatment icon  

Impact

Impact on ecosystems and waterways

Stemless thistle is commonly found in pastures, and on roadsides, channel banks and fallow ground. In Victoria, the weed is widespread and occurs in medium to large populations. It also has a major effect on native ground covers and grasses.

Agricultural and economic impacts

Stemless thistle is rarely eaten by stock therefore reducing the carrying capacity of heavily infested paddocks. However, when stock have been forced to eat the plant, cases of impaction and suspected liver damage have occurred.

Stemless thistle is not known to affect the quality of cropping produce and harvesting costs. Seeds survive in the soil for several years making eradication difficult. It has the potential to reduce land values in agricultural areas.

Social value and health impacts

The spiny nature of the stemless thistle may restrict some recreational activities. The weed's sharp spines may also cause minor injuries to humans with spines being present for much of the year.

Management

Prescribed measures for the control of noxious weeds:

  • application of a registered herbicide
  • physical removal.

Read about prescribed measures for the control of noxious weeds.

Other management techniques

Changes in land use practices and spread prevention may also support stemless thistle management after implementing the prescribed measures.

Page last updated: 26 Jun 2020