Star Thistle

Centaurea calcitrapa L.

Family: - Asteraceae.


Centaurea refers to the medicine man, Chiron, because of the medicinal properties of some plants in this genus.

Calcitrapa is from Latin meaning heel trap and refers to the similarity between the sharp, spiny caltrops that Roman soldiers threw under the feet of enemy horses and the sharp spiny flower head of this thistle.

Star Thistle - refers to the star shape of the long sharp bracts surrounding the flower.

Other Names:

Chinese Thistle

Murrayr (Lebanon)

Purple Cockspur

Purple Star Thistle

Red Star Thistle

Saucy Bob

Sterdissel (South Africa)


An erect, bushy, pale purple flowered annual to biennial, sparsely hairy thistle, with 2 cm long yellow spiny bracts under the flower heads and a striped pale green, spineless stems up to 1 m tall. The deeply divided, spineless rosette leaves are initially grey and become dark green with lighter veins with age. It flowers in summer.



Two. Club shaped. Edges smooth. Tip round to flat. Base tapered. Hairless.

First leaves:

Spear shaped. Edges toothed. Tip pointed. Base tapered. Long whitish hairs on the upper and lower surface.


Forms a rosette. Grey when young becoming dark green with age.

Stipules - none.

Petiole - rosette leaves have a short petiole, stem leaves usually don't.

Blade - Dark green with prominent lighter veins. Up to 250 mm long. Deeply divided into narrow, lance shaped, often toothed lobes, below a slender terminal lobe. Lobes up to 150 mm long. Sparse, crisp hairs initially becoming glandular hairy with age. Sunken glands on the top and bottom of leaf. No spines. Base tapered to squarish.

Stem leaves - Usually stalkless. Lower leaves lobed about half way to the midrib. Lobes narrowly egg shaped with pointed tips and teeth on the edges. Upper leaves less lobed, 10-30 mm long, lobes more parallel sided. Uppermost leaves egg shaped to arrow shaped with no lobes.


Sparse, crisp hairs and downy. Many branched from the base. Straggly, tangled, bushy, rather woody, striped. Up to 1000 mm tall. Pale green to whitish. No wings. No spines. May produce long runners in sandy soils.

Flower head:

Flower heads at the ends of branches. Hairless, slender, 10-15 x 6-10 mm (without the spines), urn shaped to cylindrical, with a few leaves underneath. Numerous, shortly stalked or stalkless. In singles on the ends of stems or in upper leaf axils. Edge (Ray) flowers sterile, central (disc) flowers bisexual. Receptacle with dense stiff hairs. No stalk or very short stalk. A few small leaves underneath. A sterile head forms in the centre of the rosette before the stem emerges.

Bracts - Leathery, numerous, hairless, egg shaped. Faintly veined. Papery edges, outermost bracts short. Intermediate bracts are egg shaped with pale bases, papery edges and a rigid, spreading, white or yellow, sharp spine that is 150-300 mm long. There are also 2-6 shorter spines at the base on fertile heads.


Tubular. Pale reddish purple, rarely pink or white. Glandular.

Ovary - inferior.

Florets - glandular

'Petals' - Pale reddish purple, rarely pink or white.

Stamens -

Anthers -


Achene. Flattened. Egg shaped, 3-4 mm long, 2 mm wide. Pale, usually with brown streaks and mottles. No pappus. Tends to remain in the head. Fruit is attached at an angle to the receptacle so they look like they have fallen over.


Whitish grey with brown streaks or blotches. Oval to tear shaped, 2 mm long by 1 mm wide. Surface smooth, shiny and hairless.


Strong, fleshy taproot, 20-30 mm diameter.

Key Characters:


Life cycle:

Annual, biennial. Flowers October to February. Reproduces by seed. Seeds germinates at any time of the year with a major germination in autumn. Rosettes form in winter, and produce a sterile flower in the centre then the stem elongate and branch in spring. Flowering is usually from October to February. Some rosettes don't produce stems and flowers until the next season, thus becoming biennial. All plants die after flowering.



By seed.

Flowering times:

November to January in SA.

Spring to summer in NSW.

October to January in WA.

Seed Biology and Germination:

Seed is short lived and will survive in the soil 2-3 years.

Tends to establish in areas where water accumulates.

Vegetative Propagules:

None, but may regrow from the crown if the top growth is damaged or from a shallowly severed taproot.



Population Dynamics and Dispersal:

Seeds tend to remain in the spiny head and are dispersed by water or attachment to stock and vehicles. The whole plant may break off at ground level and tumble in the wind.

Seed is spread in water, as a contaminant of produce and agricultural seeds, or by seed heads attaching to stock or vehicles.

Origin and History:

Southern, western and central Europe, Western Asia, North Africa.

First recorded in SA in 1862. It became a serious weed of cereals up to the 1950's but has decreased in importance as soil fertility and weed control practices have improved.




Temperate regions with 700-900mm rainfall. On many soil types. Watercourses.


Temperate regions with an annual rainfall of 700-900 mm.


Sands and many other soil types.

Plant Associations:

Open areas.



Honey plant.


Weed of roadsides, stockyards, pastures, crops, irrigated lucerne and cultivated or disturbed areas.

It competes with crops and pastures, harbour vermin when dense and injures the eyes and mouths of stock.

It is not grazed due to its spiny nature.


It is probably toxic to stock but is rarely grazed.


Noxious weed of ACT, NSW, SA, TAS, VIC.

Management and Control:


Eradication strategies:

Isolated plants should be removed manually and burnt.

It tends to be associated with poorer pastures and has decreased as soil fertility improves. Seed is short lived in the soil so it should be possible to eradicate from paddocks. Cultivation to 100 mm to cut off the taproot is effective on rosette stage plants. The effectiveness of slashing and mowing depends on timing. If done too early the plant recovers, if done too late the seeds may develop in the cut heads. Slashing pre-flowering is preferred to mowing because it damages the stems. Burning in combination with cutting provides good control. Hormone herbicides are effective on young plants and picloram is effective up to the pre-flowering stage.

Herbicide resistance:

None reported.

Biological Control:

Related plants:

Black Knapweed (Centaurea nigra)

Cornflower (Centaurea cyanus)

Dusty Miller (Centaurea cineraria)

Maltese Cockspur (Centaurea melitensis)

Panicled Knapweed (Centaurea paniculata)

St Barnaby's Thistle (Centaurea solstitialis)

Centaurea aspera

Creeping Knapweed (Acroptilon repens)

Plants of similar appearance:


Auld, B.A. and Medd R.W. (1992). Weeds. An illustrated botanical guide to the weeds of Australia. (Inkata Press, Melbourne). P90. Photo.

Black, J.M. (1965). Flora of South Australia. (Government Printer, Adelaide, South Australia). P936. Diagrams.

Burbidge, N.T. and Gray, M. (1970). Flora of the Australian Capital Territory. (Australian National University Press, Canberra). P394. Diagram.

Cunningham, G.M., Mulham, W.E., Milthorpe, P.L. and Leigh, J.H. (1992). Plants of Western New South Wales. (Inkata Press, Melbourne). P721. Photo.

Lamp, C. and Collet, F. (1990). A Field Guide to Weeds in Australia. (Inkata Press, Melbourne).

Lazarides, M. and Hince, B. (1993). CSIRO handbook of economic plants of Australia. (CSIRO, Melbourne). #278.2.

Marchant, N.G., Wheeler, J.R., Rye, B.L., Bennett, E.M., Lander, N.S. and Macfarlane, T.D. (1987). Flora of the Perth Region. (Western Australian Herbarium, Department of Agriculture, Western Australia). P666.

Moerkerk, M.R. and Barnett A.G. (1998) More Crop Weeds. (R.G and F.J. Richardson, Melbourne). P54. Photos. Diagrams.

Parsons, W.T. and Cuthbertson, E.G. (1992). Noxious weeds of Australia. (Inkata Press, Melbourne). P199-201. Photos.


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