Identification and Reproduction

Identification: 

• Slenderflower thistle is a winter annual that is similar in appearance to the Italian thistle.
• Stems can grow up to 1.8 m tall, triangular and covered in spines and purple flecks.

• Leaves are deeply lobed and spiny, undersides are covered in cobwebby hairs. 
• Terminal flowers appear in clusters of 5-20. They are small (2.5 cm), slender and pink to purple in colour. Flowerheads are covered in long spiny bracts. 

• It flowers in early spring until summer; April-July. 

Reproduction: 

It reproduces by seed, which are easily dispersed by wind. 

Habitat & Ecology

• This plant is found along roadsides, fields and recently disturbed sites. 
• It prefers recently disturbed sites, particularly sites that have been recently burned.
• It thrives in fertile soils with moist conditions. 

Impacts

Social: 

• Reduces foliage availability and displaces native species. 
• Displaces desired crop species. 
• Can limit the mobility and injure livestock. 
• Spines and dead leaves have also been prone to contaminating wool. 

Ecological: 

• This aggressive plant forms dense stands that displace native vegetation. 

Management

Prevention is a high priority for this plant. 

Mechanical/Manual Control:

• Mowing is only effective prior to seedset. It may need to be repeated for at least 3 years to exhaust the existing seed bank. 

Resources

For more information check out BugwoodWiki's datasheet on Slenderflower thistle. 

Check out the Agriculture of Victoria's fact page for Slender Thistle for more information on control measures here. 

Header photo (Javiar martin).