Quick Facts

Quick facts

  • Originally from Mediterranean region, western Asia and the Middle East, St Barnaby's Thistle (Centaurea solstitialis) is an erect annual or biennial or a short lived perennial herb with yellow flowers surrounded by spines 
  • Invades pasture, crops and disturbed areas.
  • Its seeds can be dispersed by wind or water or spread as a contaminant of agricultural produce including commercial seed, wool and fodder or via vehicles and machinery.
  • Native grass species may compete strongly with St Barnaby's Thistle and prevent invasion in native grasslands.
  • Control with herbicides, cultivation or slashing and mowing to prevent seed set.
  • Treatment with bio-control agents has potential.

What Does It Look Like?

What is it?

St Barnaby's Thistle (Centaurea solstitialis) is an erect annual or biennial herb, which grows up to 750 mm occasionally to 1 metre high. It initially forms a basal rosette (radiating cluster) of short-lived leaves, 200 mm long and and 60 mm wide. Rosette leaves are pinnately lobed to lyrate (deeply lobed, with a large terminal lobe and smaller lateral ones) that vary considerably in shape. Rosette leaves are pubescent (downy; covered with short, soft, erect hairs) to cobwebbed, margins rough to touch.  One to several much-branched stems arise from the centre of the rosette growing to 1 metre tall. Stems are all winged and covered with fine hairs which give them a cottony or downy appearance. The stem leaves grow to 10–70 mm long, are narrow, and clasp the stem, normally bigger leaves at the base, that are toothed to lobed or with entire margins (i.e. smooth edged, not lobed),smaller leaves at he top of the plant with entire margins (i.e. smooth edged, not lobed). The leaves between these are intermediate and can also be slightly lobed. All the stems and leaves have a greyish appearance due to the presence of hairs (Parsons & Cuthbertson 2001; Navie 2004).

The flower heads are egg-shaped, with many densely packed flowers (looks like one many-petal flower) all with bright yellow petals (corolla). Flower heads are 15–20 mm long, and up to 15 mm across. They occur at the end of branches and are surrounded by a group of bracts (modified leaves) also known as an involucre 10–12 mm long. The outer bracts are ovate (egg-shaped), covered in cobwebbed hairs to glabrous (smooth without hairs), with a straight stout spine at the end 10–25 mm long with 1 or 2 pairs of smaller basal spines. Inner bracts with tough to the touch with round teeth at the apex.  Each flower produces a seed with many seeds produced on a flower-head. Flowers mainly Nov–Feb.

The fruits or 'seeds' (cypselas) are are produced in the flower head and there are two types of seeds. The outer seeds are dark brown or blackish, 3–4 mm long, mottled and usually without bristles; the inner seeds are grey or light brown, 2–3 mm long, glossy and topped with a pappus (tuft) of numerous whitish bristles 2–5 mm long (Parsons & Cuthbertson 2001; Navie 2004).

For further information and assistance with identification of St Barnaby's Thistle, contact the herbarium in your state or territory.

Flower colour


Growth form (weed type/habit)


Where it currently grows? Preferred habitat

St Barnaby's Thistle usually occupies sub-coastal temperate and sub-tropical regions with an annual rainfall above 600 mm but can also be present in semi-arid environments along roadsides and waste places. It inhabits pastures, rangelands, crops, fallows as well as waste areas, disturbed sites and roadsides. It occasionally invades unimproved grazing land (Parsons & Cuthbertson 2001; Navie 2004).

Are there similar species?

St Barnaby's Thistle is very similar to Maltese Cockspur (Centaurea melitensis). It is also relatively similar to Saffron Thistle (Carthamus lanatus), African Thistle (Berkheya rigida), Golden Thistle (Scolymus hispanicus), Spotted Thistle (Scolymus maculatus), Star Thistle (Centaurea calcitrapa) and Glaucous Star Thistle (Carthamus leucocaulos).

Maltese Cockspur (Centaurea melitensis) differs from St Barnaby's Thistle mainly by having reddish spines of almost uniform size on the bracts (Navie 2004).

Saffron Thistle (Carthamus lanatus), African Thistle (Berkheya rigida) and Star Thistle (Centaurea calcitrapa) all have wingless stems whereas St Barnaby's Thistle has winged stems (Navie 2004).

Golden Thistle (Scolymus hispanicus) and Spotted Thistle (Scolymus maculatus) both have spiny stems whereas St Barnaby's Thistle does not (Navie 2004).

Glaucous Star Thistle (Carthamus leucocaulos) is not hairy whereas St Barnaby's thistle stems are covered with fine hairs (Navie 2004).

Star Thistle (Centaurea calcitrapa) and Glaucous Star Thistle (Carthamus leucocaulos)  have purple flowers unlike St Barnaby's Thistle which has yellow flowers (Navie 2004).

Why Is It A Weed?

What are its impacts?

St Barnaby's Thistle (Centaurea solstitialis) will out-compete crops and pastures and dense patches can restrict stock movement in areas where rainfall is above 600 mm. In drier areas will invade roadside waste land and unimproved pastures.  

Reports from the United States suggest that the rosettes are toxic to horses and cause a neurological disorder. Similar symptoms have been noted occasionally in Australia (Parsons & Cuthbertson 2001; SNWCB 2007).

Agriculture: St Barnaby's Thistle is not readily eaten by livestock except when very young. Overseas evidence reports that plants compete with useful pastures, by producing chemicals which may reduce germination of its own seeds and restrict growth of other species, both of which place it at a competitive advantage. This effect reduces the carrying capacity of the land (Parsons & Cuthbertson 2001). Plants of this species often occur in dense patches which restrict stock movement and can injure dogs, humans and grazing animals, particularly in the eyes, mouth and feet, and contribute to vegetable fault in wool (Parsons & Cuthbertson 2001). St Barnaby's Thistle inhabits pastures, rangelands, crops, fallows as well as waste areas, disturbed sites and roadsides and occasionally invades unimproved grazing land (Parsons & Cuthbertson 2001; Navie 2004).

Native ecosystems: St. Barnaby's thistle (Centaurea solstitialis) can form dense impenetrable stands that displace desirable vegetation in natural grasslands, rangelands. This can lead to a reduction in the habitat available to wildlife and decrease the native plant and animal diversity in densely infested areas.

Urban areas: A weed of roadsides and neglected sites especially in drier areas. 

How does it spread?

St Barnaby's Thistle is only spread by seed, some of which have a pappus present which facilitates wind dispersal. Seed can also be spread by water or as a contaminant of agricultural produce including commercial seed, wool and fodder and via vehicles and machinery (Parsons & Cuthbertson 2001).

What is its history in Australia?

St Barnaby's Thistle was first recorded in Victoria as early as 1856 but the circumstance of its introduction is unknown (Parsons & Cuthbertson 2001).

First collected in South Australia in Adelaide in 1880, in Queensland in 1882, and in Victoria in 1889, and in New South Wales in 1902 (AVH 2021).

How To Manage It?

Best practice management

St Barnaby's Thistle (Centaurea solstitialis) can be controlled by herbicides when plants are young, by cultivation and by pasture management.

Chemical control:  Herbicide application at the seedling or immature growth stage can also control this species (Parsons & Cuthbertson 2001). See DPI NSW (2019) for further herbicide information. Please also check the Australian Pesticides and Veterinary Medicines Authority for chemical information http://www.apvma.gov.au.

Non-chemical control: Physical control: Single plants or small populations can be removed by hand or chipping out if recently new to an area. 

Mechanical control: Seedlings and immature plants are controlled by shallow cultivation but this must be repeated to deal with the subsequent germination (Parsons & Cuthbertson 2001). Mowing or slashing can help manage St Barnaby's Thistle, however, this should be done at the right time, too early and plants may regrow and set seed, and to late when in flower may allow seeds too mature on cut material.

Competition and management: Effective control can be maintained by encouraging legume-based pastures which, with adequate fertiliser, provide maximum competition to the weed (Parsons & Cuthbertson 2001). Experiments have shown that the common native ringed wallaby grass (Rytidosperma caespitosum) [as Austrodanthonia caespitosa] competes strongly with St Barnaby's Thistle and may be a factor in preventing invasion of South Australia's native grasslands (Hay et al. 2006). Other studies suggest nutrients, seed origin (seed from overseas may be more competitive that Australian seed) and identity of competing species are important factors in preventing invasion of Australian grasslands by St Barnaby's Thistle (Hay et al. 2007).

Does it have a biological control agent?


When does it grow? (lifecycle/growth calendar)

St Barnaby's Thistle reproduces by seed which germinate in autumn. Seedlings develop into rosettes over winter, reaching about 30–40 mm diameter by spring. The stems are produced in spring and flowering commences in about November and continues into summer. Seeds are produced over a period of 4 or 5 months before the plants die. In mild summers the roots may stay alive and produce a new rosette in the autumn, from which flowering stems are again produced in the second summer (Parsons & Cuthbertson 2001).

St Barnaby's Thistle has been estimated to produce approximately 1,400 to 13,000 seed per square metre and spreads at a rate of about 2,800 to 8,000 hectares per year in the United States (Widmer & Guermache 2007).

Where Is It Found?

Which states and territories is it found?

Found in all Australian states and territories.

What areas within states and territories is it found?

St Barnaby's Thistle is well established throughout New South Wales.

In Victoria established in patches from Albury to Bendigo.

In  Queensland established and localised in patches in the Warwick and Toowoomba areas and surrounds.

in South Australia established in and around Adelaide and in the hills to just south of Port Augusta (AVH 2021).

It is also recorded from Tasmania, Western Australia and from one locality in the Northern Territory (Parsons & Cuthbertson 2001; Navie 2004; AVH 2021).

Where does it originate?

St Barnaby's Thistle is native to the Mediterranean region and western Asia (Parsons & Cuthbertson 2001) and the Middle East (POWO 2019).

National And State Weed Listings

Is it a Weed of National Significance (WONS)?


Where is it a declared weed?


Government weed strategies and lists – Weeds Australia

Is it on the National Alert List for Environmental Weeds?


Government weed strategies and lists – Weeds Australia

Is it on the Agricultural Sleeper List?


Government weed strategies and lists – Weeds Australia

Names And Taxonomy

Main scientific name

Centaurea solstitialis

Other scientific names (synonyms)?


Does it have other known common name(s)?

Barnaby's Thistle, Golden Star Thistle, Golden Starthistle, Yellow Star Thistle, Yellow Star-thistle, Yellow Starthistle, Geeldissel, Yellow Centaurea, Yellow Cockspur, Knapweed

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