Silybum marianum (L.) Gaertn., Asteraceae

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Present on Pacific Islands?  yes

Primarily a threat at high elevations?  no

Risk assessment results:  High risk, score: 17.5 (Go to the risk assessment)

Other Latin names:  Carduus marianus L.

Common name(s): [more details]

English: blessed milk thistle, gundagai thistle, holy thistle, lady's thistle, milk thistle, spotted thistle, variegated thistle

French: chardon-Marie, silybe de Marie

Spanish: cardo de María, cardo lechero, cardo mariano, cardo santo

Habit:  herb

Description:  "Annual or biennial. Stems branched above, ridged, with sparse mealy hairs at least above, 0.5-2 m tall, not winged. Leaves elliptic to lanceolate, lyrate-pinnatifid to pinnate, sinuate, coarsely dentate, green with conspicuous white markings along veins, (10)-20-60 x (5)-10-30 cm, with sparse short mealy hairs on lamina, and sparse long tangled multicellular hairs on midrib; base amplexicaul, auriculate, with very spinous margins; prickles marginal, yellowish, spreading, 5-12 mm long. Capitula ovoid, erect, 4-6 x 5-7 cm, solitary, terminal and pedunculate, and also sessile in axils of uppermost leaves; peduncles with appressed cobwebby tomentum. Involucral bracts sparsely covered with short mealy hairs; margins with sparse cobwebby hairs. Outer bracts leaflike, obovate with spinous apex and margins. Middle bracts oblong; appendage ovate, subulate, with spinous margins and a long spreading to recurved apical spine. Inner bracts lanceolate; appendage becoming linear-lanceolate, entire. Corolla reddish purple, 20-28 mm long; lobes unequal, 4-6 mm long. Anther filaments joined at margins into a tube which encloses the basal appendages of the anthers. Style exserted 1-2 mm beyond corolla lobes. Achenes brown or black-streaked, obovoid, weakly transversely flattened, smooth, c. 6 x 3 mm; outer pappus bristles scabrid, c. 15 mm long; inner hairs very fine"  (Webb et al., 1988; 316).

Habitat/ecology:  "Grassland, coastal scrub and dunes, riparian habitats.  This plant occurs frequently in disturbed sites and is invasive because the large rosettes shade out native plants and form extensive patches that crowd out native vegetation and impede wildlife.  The plant spreads quickly once establish and may for an impenetrable cover over large areas.  Dead plants leave spots of bare soil that may become colonized by this plant or other weeds"  (Weber, 2003; p. 403).

In New Zealand, "roadsides, pastures, gardens, waste land"  (Webb et al., 1988; 316).  In Australia, "a noxious weed of roadsides, wasteland etc."  (Flora of Australia online).

Propagation:  "Seeds are dispersed by attaching to animals, by water and in mud.  Seeds may remain viable for 10 years"  (Weber, 2003; p. 403).

Native range:  Europe, Israel, Turkey, Egypt; naturalized elsewhere (GRIN).

Presence:

Pacific
Country/Terr./St. & Island group	Location	Cited status & Cited as invasive & Cited as cultivated & Cited as aboriginal introduction?	Reference & Comments
Australia (Pacific offshore islands) Lord Howe Island	Lord Howe Island	introduced invasive	Australian Biological Resources Study (2013) Voucher cited: J. Pickard 3536 (NSW)
Australia (Pacific offshore islands) Norfolk Islands	Norfolk Island	introduced invasive	Australian Biological Resources Study (2013) Voucher cited: W.R. Sykes NI 488 (CHR)
Chile (offshore islands) Juan Fernández Islands	Isla Más a Tierra (Robinson Crusoe Island)	introduced invasive	Skottsberg, Carl (1953) (p. 225) Very abundant in the bottom of valleys from Pto Frances to El Puente and also on the south side of the island; one of the dangerous weeds.
Chile (offshore islands) Juan Fernández Islands	Isla Más a Tierra (Robinson Crusoe Island)	introduced invasive	Atkinson, Rachel/Sawyer, John (2011)
Chile (offshore islands) Juan Fernández Islands	Isla Más a Tierra (Robinson Crusoe Island)	introduced invasive	Danton, Philippe/Perrier, Christophe/Martinez Reyes, Guido (2006) (p. 557)
Chile (offshore islands) Juan Fernández Islands	Isla Más Afuera (Alejandro Selkirk Island)	introduced	Skottsberg, Carl (1953) (p. 225)
Chile (offshore islands) Juan Fernández Islands	Isla Más Afuera (Alejandro Selkirk Island)	introduced invasive	Atkinson, Rachel/Sawyer, John (2011)
Chile (offshore islands) Juan Fernández Islands	Isla Más Afuera (Alejandro Selkirk Island)	introduced invasive	Danton, Philippe/Perrier, Christophe/Martinez Reyes, Guido (2006) (p. 557)
Chile (offshore islands) Juan Fernández Islands	Isla Santa Clara	introduced invasive	Atkinson, Rachel/Sawyer, John (2011)
Chile (offshore islands) Juan Fernández Islands	Isla Santa Clara	introduced invasive	Danton, Philippe/Perrier, Christophe/Martinez Reyes, Guido (2006) (p. 557)

Pacific Rim
Country/Terr./St. & Island group	Location	Cited status & Cited as invasive & Cited as cultivated & Cited as aboriginal introduction?	Reference & Comments
Australia Australia (continental)	New South Wales	introduced invasive	National Herbarium of New South Wales (2013)
Australia Australia (continental)	Australia (continental)	introduced	U.S. Dept. Agr., Agr. Res. Serv. (2013)
British Columbia (province of Canada) Province of British Columbia	Canada (British Columbia)	introduced invasive	U.S. Dept. Agr., Nat. Res. Cons. Serv. (2013)
Japan Japan	Japan	introduced	Mito, Toshikazu/Uesugi, Tetsuro (2004) (p. 190)
New Zealand New Zealand	New Zealand (country)	introduced invasive	Webb, C. J./Sykes, W. R./Garnock-Jones, P. J. (1988) (p. 316)
South America (Pacific rim) South America (Pacific rim)	Chile (Republic of)	introduced	Skottsberg, Carl (1953) (p. 225)
United States (west coast) United States (west coast states)	USA (Oregon)	introduced invasive	U.S. Dept. Agr., Nat. Res. Cons. Serv. (2013)
United States (west coast) United States (west coast states)	USA (California)	introduced invasive	U.S. Dept. Agr., Nat. Res. Cons. Serv. (2013)
United States (west coast) United States (west coast states)	USA (Washington)	introduced invasive	U.S. Dept. Agr., Nat. Res. Cons. Serv. (2013)

Also reported from
Country/Terr./St. & Island group	Location	Cited status & Cited as invasive & Cited as cultivated & Cited as aboriginal introduction?	Reference & Comments
Canada Canada	Canada	introduced invasive	U.S. Dept. Agr., Nat. Res. Cons. Serv. (2013)
United States (continental except west coast) United States (other states)	United States (other states)	introduced invasive	U.S. Dept. Agr., Nat. Res. Cons. Serv. (2013)

Control: 

Physical:  "Mowing before fruit formation prevents seed dispersal.  Planting desirable species suppresses seedling establishment of this plant".

Chemical:  "Chemical control is most effective at the seedling and rosette stages.  An effective herbicide is 2,4-D ester"  (Weber, 2003; p. 403).