Silybum marianum

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Milk thistle
Milk thistle flowerhead.jpg
Scientific classification edit
Kingdom: Plantae
Clade: Tracheophytes
Clade: Angiosperms
Clade: Eudicots
Clade: Asterids
Order: Asterales
Family: Asteraceae
Genus: Silybum
S. marianum
Binomial name
Silybum marianum
(L.) Gaertn.

Carduus marianus L.

Silybum marianum has other common names including cardus marianus, milk thistle,[1] blessed milkthistle,[2] Marian thistle, Mary thistle, Saint Mary's thistle, Mediterranean milk thistle, variegated thistle and Scotch thistle (though not to be confused with Onopordum acanthium or Cirsium vulgare). This species is an annual or biennial plant of the family Asteraceae. This fairly typical thistle has red to purple flowers and shiny pale green leaves with white veins. Originally a native of Southern Europe through to Asia, it is now found throughout the world.



Milk thistle is an upright herb that can grow to be 30 to 200 cm (12 to 79 in) tall and has an overall conical shape.[3] The approximate maximum base diameter is 160 cm (63 in). The stem is grooved and may be covered in a light cottony fuzz.[4] The largest specimens have hollow stems.

The leaves are oblong to lanceolate and 15–60 cm long and typically pinnately lobed, with spiny edges like most thistles.[3] They are hairless, shiny green, with milk-white veins.[3]

The flower heads are 4 to 12 cm long and wide, of red-purple colour. They flower from June to August in the North or December to February in the Southern Hemisphere (summer through autumn).[4] The flower head is surround by bracts which are hairless, with triangular, spine-edged appendages, tipped with a stout yellow spine.

The fruits are black achenes with a simple long white pappus, surrounded by a yellow basal ring.[5][3] A long pappus acts as a "parachute", supporting seed dispersal by wind.[6]

Distribution and habitat[edit]

S. marianum is native to the Mediterranean region of Europe including Greece (mostly in Crete), east into Iran and Afghanistan.[4][7] It is possibly native near the coast of southeast England. S. marianum has been widely introduced outside its natural range, for example into North America, Hawaii, Australia, New Zealand, Colombia where it is considered an invasive weed.[4][8][9]

Milk thistle has been potentially observed to modify fire regimes in its invasive range.[10][11] Its invasion into new habitats may also be encouraged by fire.[12]

The "giant thistle of the Pampas" reported by Darwin in the Voyage of the Beagle[13] is thought by some to be Silybum marianum.[14][15]


Traditional milk thistle extract is made from the seeds, which contain approximately 4–6% silymarin.[16] The extract consists of about 65–80% silymarin (a flavonolignan complex) and 20–35% fatty acids, including linoleic acid.[17] Silymarin is a complex mixture of polyphenolic molecules, including seven closely related flavonolignans (silybin A, silybin B, isosilybin A, isosilybin B, silychristin, isosilychristin, silydianin) and one flavonoid (taxifolin).[17] Silibinin, a semipurified fraction of silymarin, is primarily a mixture of 2 diastereoisomers, silybin A and silybin B, in a roughly 1:1 ratio.[17][18]

Traditional medicine and adverse effects[edit]

Although milk thistle has been used in traditional medicine for centuries, there is no clinical evidence that it has any medicinal effect, and the quality of research has been poor.[19][20][21] Use of milk thistle may cause stomach upset and produce allergic reactions in some people.[19]

In 2019, Cancer Research UK stated: "We need a lot more research with reliable clinical trials before we can be sure that milk thistle will play any part in treating or preventing cancers."[22]


Milk thistle based supplements have been measured to have the highest mycotoxin concentrations of up to 37 mg/kg when compared to various plant-based dietary supplements.[23]

Animal toxicity[edit]

Because of nitrate[4] content, the plant has been found to be toxic to cattle and sheep.[4] When potassium nitrate is eaten by ruminants, the bacteria in the animal's stomach breaks the chemical down, producing nitrite ions. Nitrite ions then combine with hemoglobin to produce methemoglobin, blocking the transport of oxygen. The result is a form of oxygen deprivation.[24]


  1. ^ BSBI List 2007 (xls). Botanical Society of Britain and Ireland. Archived from the original (xls) on 2015-06-26. Retrieved 2014-10-17.
  2. ^ "Silphium marianum". Natural Resources Conservation Service PLANTS Database. USDA. Retrieved 15 November 2015.
  3. ^ a b c d Flora of North America Editorial Committee (ed.). "Silybum marianum". Flora of North America North of Mexico (FNA). New York and Oxford – via, Missouri Botanical Garden, St. Louis, MO & Harvard University Herbaria, Cambridge, MA.
  4. ^ a b c d e f Flora of Australia Volume 37 : Asteraceae. Melbourne: CSIRO Publishing. 2015. ISBN 9781486304158. Retrieved 9 August 2020.
  5. ^ Rose, Francis (1981). The Wild Flower Key. Frederick Warne. pp. 388–9. ISBN 978-0-7232-2419-8.
  6. ^ "Milk Thistle". Fraser Valley Invasive Species Society. Retrieved 24 January 2021.
  7. ^ Jahn, Ralf; Schoenfelder, Peter (1995). Exkursionsflora für Kreta. E. Ulmer. ISBN 978-3800134786.
  8. ^ Bernal; Gradstein; Celis (2019). Catálogo de plantas y líquenes de Colombia. Bogotá: Instituto de Ciencias Naturales, Universidad Nacional de Colombia.
  9. ^ "Silybum marianum". plantpono. Retrieved 9 August 2020.
  10. ^ Lambert, Adam; D'antonio, Carla; Dudley, Tom (2010). "Invasive species and fire in California ecosystems". Fremontia. 38 (2): 29–36. CiteSeerX
  11. ^ Knapp, John (2010). "CATALINA ISLAND'S INVASIVE PLANT MANAGEMENT PROGRAM, WITH AN EMPHASIS ON INVASION AND PROTECTION OF OAK ECOSYSTEMS" (PDF). Catalina Island Conservancy. Proceedings of an on-island workshop, February 2–4, 2007: 35–46. Retrieved 9 August 2020.
  12. ^ Bean, Caitiln. "ELEMENT STEWARDSHIP ABSTRACT for Silybum marianum" (PDF). The Nature Conservancy. Retrieved 9 August 2020.
  13. ^ Darwin, Charles Robert. The Voyage of the Beagle. Vol. XXIX. The Harvard Classics. New York: P.F. Collier & Son, 1909–14;, 2001. [accessed 30 Sep 2016] Ch VI.
  14. ^ Bulletin of the Torrey Botanical Club (Torrey Botanical Club, 1887), p. 163
  15. ^ The Rise of Capitalism on the Pampas: The Estancias of Buenos Aires, 1785-1870, By Samuel Amaral (Cambridge University Press,2002) p. 129
    "Charles Darwin, who visited the pampas while traveling around the world, refers to Cynara cardunculus as cardoon, differentiating it from the great thistle, which scientific designation does not mention, described by F. B. Head. The former was as high as a horse; the second, higher than the head of a horserider. In Far Away and Long Ago, William Henry Hudson mentions two types: the cardoon thistle, or wild artichoke, of a bluish or grey-greenish color, and the giant thistle, cardo asnal for the natives and Carduus marianum for botanists, with white and green leaves."
  16. ^ Greenlee, H.; Abascal, K.; Yarnell, E.; Ladas, E. (2007). "Clinical Applications of Silybum marianum in Oncology". Integrative Cancer Therapies. 6 (2): 158–65. doi:10.1177/1534735407301727. PMID 17548794.
  17. ^ a b c Kroll, D. J.; Shaw, H. S.; Oberlies, N. H. (2007). "Milk Thistle Nomenclature: Why It Matters in Cancer Research and Pharmacokinetic Studies". Integrative Cancer Therapies. 6 (2): 110–9. doi:10.1177/1534735407301825. PMID 17548790.
  18. ^ Hogan, Fawn S.; Krishnegowda, Naveen K.; Mikhailova, Margarita; Kahlenberg, Morton S. (2007). "Flavonoid, Silibinin, Inhibits Proliferation and Promotes Cell-Cycle Arrest of Human Colon Cancer". Journal of Surgical Research. 143 (1): 58–65. doi:10.1016/j.jss.2007.03.080. PMID 17950073.
  19. ^ a b "Milk thistle". National Center for Complementary and Integrative Health, US National Institutes of Health. 1 August 2020. Retrieved 20 October 2020.
  20. ^ Rainone, Francine (2005). "Milk Thistle". American Family Physician. 72 (7): 1285–8. PMID 16225032.
  21. ^ Rambaldi A, Jacobs BP, Gluud C (2007). "Milk thistle for alcoholic and/or hepatitis B or C virus liver diseases". The Cochrane Database of Systematic Reviews (4): CD003620. doi:10.1002/14651858.CD003620.pub3. PMID 17943794.
  22. ^ "Milk thistle and liver cancer". Cancer Research UK. 9 May 2019. Retrieved 9 August 2020.
  23. ^ Veprikova Z, Zachariasova M, Dzuman Z, Zachariasova A, Fenclova M, Slavikova P, Vaclavikova M, Mastovska K, Hengst D, Hajslova J (2015). "Mycotoxins in Plant-Based Dietary Supplements: Hidden Health Risk for Consumers". Journal of Agricultural and Food Chemistry. 63 (29): 6633–43. doi:10.1021/acs.jafc.5b02105. PMID 26168136. The highest mycotoxin concentrations were found in milk thistle-based supplements (up to 37 mg/kg in the sum).
  24. ^ Tucker JM, et al. Nitrate Poisoning in Livestock (1961)

Further reading[edit]