Carduus marianus L.
Silybum marianum has other common names including cardus marianus, milk thistle, blessed milkthistle, 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. The approximate maximum base diameter is 160 cm (63 in). The stem is grooved and may be covered in a light cottony fuzz. The largest specimens have hollow stems.
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). The flower head is surround by bracts which are hairless, with triangular, spine-edged appendages, tipped with a stout yellow spine.
Distribution and habitat
S. marianum is native to the Mediterranean region of Europe including Greece (mostly in Crete), east into Iran and Afghanistan. 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.
Traditional milk thistle extract is made from the seeds, which contain approximately 4–6% silymarin. The extract consists of about 65–80% silymarin (a flavonolignan complex) and 20–35% fatty acids, including linoleic acid. 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). Silibinin, a semipurified fraction of silymarin, is primarily a mixture of 2 diastereoisomers, silybin A and silybin B, in a roughly 1:1 ratio.
Traditional medicine and adverse effects
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. Use of milk thistle may cause stomach upset and produce allergic reactions in some people.
Because of nitrate content, the plant has been found to be toxic to cattle and sheep. 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.
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"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."
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The highest mycotoxin concentrations were found in milk thistle-based supplements (up to 37 mg/kg in the sum).
- http://ucanr.edu/sites/UCCE_LR/files/180507.pdf Tucker JM, et al. Nitrate Poisoning in Livestock (1961)
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