Quick Facts

Quick facts

• Originally from the Mediterranean region, Glaucous Star Thistle (Carthamus leucocaulos) is an upright annual herb with pale pink to violet flowers and spine-tipped leaves.
• It is not widespread in Australia at present but has the potential to become a serious weed similar to Saffron Thistle.
• It is highly competitive with cereal crops and desirable Rangeland species.
• It has little food value for animals and in dense patches restricts stock movement.
• The seed is not wind dispersed, most seed falling close to the parent plant.
• Spread by attaching to the fur of animals, particularly sheep.
• Controlled by cultivation and herbicides.

What Does It Look Like?

What is it?

Glaucous Star Thistle (Carthamus leucocaulos) is an erect stiff spiny annual herb 35–80 cm high. Its stems are white to greyish in colour and shiny with longitudinal ribs and sparse, initially with yellow to white glandular hairs becoming hairless with age. Its first leaves rosette leaves are short-lived whorled leaves radiating from a central point more or less flat on ground, with deeply divided with lobes, each lobe ending in a short stout spine. Stiff rigid spiny stem leaves are deeply divided into lobes, each lobe ending in a stiff stout yellow-brown spine. Stem leaves are smaller, 30–60 mm long and 5–15 mm wide, grey-green above and below, glandular, without hairs to sparsely hairy.

The flowers are pale violet to pinkish purple 20–30 mm long, arranged in dense clusters of flower-heads (capitula) and each flowers head is solitary at the end of branches. Flower-heads are 13–15 mm diameter, surrounded by bracts (leaf-like organs surrounding the flower-heads) and outer bracts are rigid and spine-tipped, densely grey-villous, inner bracts entire, erect, margins dry and membranous (scarious), densely glandular, spine-tipped. Each flower produces a seed with many seeds produced on a flower-head.

The fruits or 'seeds' (cypselas) are 3–4 mm long, pale, grey-brown, smooth, 4-angled with a  tuft of linear acuminate (tapering gradually to a point) scales (pappus), the longest 5–6 mm (Walsh & Entwisle 1999; Parsons & Cuthbertson 2001; Navie 2004). Flowers spring and summer.

For further information and assistance with identification of Glaucous Star Thistle, contact the herbarium in your state or territory.

Flower colour

Purple or Pink

Growth form (weed type/habit)

Herb

Where it currently grows? Preferred habitat

In Australia, Glaucous Star Thistle occurs in disturbed areas on roadsides, in cultivated fields, degraded pastures and waste places (Parsons & Cuthbertson 2001).

Are there similar species?

The shiny, white to greyish stems of Glaucous Star Thistle (Carthamus leucocaulos) should separate it from the three other species of Carthamus growing in Australia: Safflower (Carthamus tinctorius), Toothed Thistle (C. dentatus) and Saffron Thistle (C. lanatus).

Glaucous Star Thistle is most likely to be confused with Toothed Thistle (Carthamus dentatus) as both species have pinkish purple flowers. The stems of Toothed Thistle are densely covered in glandular hairs, while the stems in Glaucous Star Thistle are almost hairless or sparsely hairy.

Glaucous Star Thistle  also resembles the widespread Saffron Thistle (Carthamus lanatus). Saffron Thistle has yellow flowers, while Glaucous Star Thistle has pale violet to pinkish purple flowers.

Safflower (Carthamus tinctorius) is easily separated by having bright orange to yellow flowers and more or less entire leaves, compared to the deeply lobed leaves of Glaucous Star Thistle (Walsh & Entwisle 1999; Navie 2004).

Why Is It A Weed?

What are its impacts?

Glaucous Star Thistle (Carthamus leucocaulos) is a noxious winter annual. It is capable of growing in dense thick patches and eliminating all other vegetation. weed of pastures, native grasslands and crops (DPI NSW 2019).

Agriculture: It is highly competitive with cereal crops and desirable rangeland species. In pasture situations, it can reduce carrying capacity (DPI NSW 2019), and because of its spiny nature, Glaucous Star Thistle can injure the eyes and mouths of livestock forced to graze within dense populations of the weeds (Brinkley & Bomford 2002). In addition, the presence of seeds, leaf fragments and flower heads contaminate wool reducing the value of the clip. In cropping it can also interfere with harvesting by blocking or damaging machinery (Parsons & Cuthbertson 2001).

Native ecosystems: It can invade degraded ecosystems, especially pen woodland and grasslands.

Urban areas: A weed of roadsides and waste places especially in poorer or degraded soils.

How does it spread?

Most of the seed from Glaucous Star Thistle falls close to the parent plant and is spread by attaching to the fur of animals, particularly sheep. The seeds of Glaucous Star Thistle have relatively long scales attached to one end, rather than hairs, so wind tends not to disperse it. It may also be spread by contaminated soil attaching to machinery or animal hooves and by the contamination of cereal grain or pasture hay (Parsons & Cuthbertson 2001; Navie 2004; Bean unpublished).

What is its history in Australia?

It is not known how Glaucous Star Thistle was introduced into Australia. The first recorded collection is from south-eastern South Australia in 1909 (AVH 2021).

How To Manage It?

Best practice management

The recommended control of Glaucous Star Thistle is the same as it is for Saffron Thistle (Carthamus lanatus), with a preferred rotation of a 2-3 years cropping phase followed by pasture. It can also be controlled by mechanical and chemical means. Good weed hygiene prevents spread of seed on machinery and vehicles.

Chemical control: In the crop, weeds should be controlled with herbicides to prevent further seeding (Dellow 1996; Woodburn et al. 1996; Parsons & Cuthbertson 2001; Department of Agriculture and Food 2007). There are various herbicides available for effective chemical treatments as for Saffron Thistle.  Control is often difficult because there are a range of plants at different growth stages. Spot spray for smaller patches and boom spray for larger areas. Seedlings which emerge in the crop can be controlled with herbicide (Parsons & Cuthbertson 2001). For information on herbicide treatments please see treatment for Saffron Thistle:  DPIPWE Tasmania (2019); DPI NSW (2019); HerbiGuide (2021); Parsons & Cuthbertson( 2001); Tamar Valley Weed Strategy (2015) Please 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.  However, not normally practical as this species seems to occurs in larger numbers than one or few individuals.

Does it have a biological control agent?

NO

When does it grow? (lifecycle/growth calendar)

Seeds germinate in autumn or early winter develop into a rosette during winter. Growth continues slowly until spring when flowers are initiated late spring and summer. Flowering begins in November or December. Seeds ripen quickly in early summer and the plant then dies, leaving the stiff stems standing (DPI NSW 2019; Parsons & Cuthbertson 2001).

Where Is It Found?

Which states and territories is it found?

SA, VIC, WA

What areas within states and territories is it found?

Glaucous Star Thistle is recorded from just east of Wartook near the Grampians and a few other scattered sites in western Victoria (AVH 2021).

Also collected from South Australia stretching from the Bordertown region and south of Naracoorte. Also known from  Kangaroo Island from Baudin Conservation Park and Pelican Lagoon Conservation Park, both on Dudley Peninsula (AVH 2021).

It is known to occur in the East Tambellup region of Western Australia (Western Australian Herbarium 1998-).

Where does it originate?

Glaucous Star Thistle is native to the Mediterranean region (Navie 2004).

National And State Weed Listings

Is it a Weed of National Significance (WONS)?

NO

Where is it a declared weed?

Not declared in any Australian state or territory.

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

Carthamus leucocaulos

Other scientific names (synonyms)?

• Kentrophyllum leucocaulon (Sm.) Tausch
• Onobroma leucocaulon (Sm.) Spreng.
• Carthamus glaucus M.Bieb. (misapplied by Jeanes, J.A. 1999, Flora of Victoria. 4: 676, Fig. 129f.; Willis, J.H. 1973, A Handbook to Plants in Victoria Edn 2. 2: 766.; Cooke, D.A. 1986, Flora of South Australia Edn 4. 3: 1630.)

Does it have other known common name(s)?

Whitestem Distaff Thistle, Distaff Thistle