No relation to : Purple Milk Vetch,
Purple Milkwort, Chalk Milkwort, Common Milkwort,Heath Milkwort or Sea Milkwort, [plants with similar names but belonging to differing Families]
Not to be confused with: Smooth Sow-Thistle which also belongs to the same Daisy and Dandelion family, and also exudes a milky white sap when damaged. But Smooth Sow-Thistle has yellow dandelion-type flowers, rather than purple thistle-type flowers.
Some similarities to : the garden variety of Rare Lords-and-Ladies [the leaves have similar milky markings] and to
Artichoke (the flower heads have similarly vicious phyllaries).
Uniquely identifiable characteristics
Distinguishing Feature : A thistle-type plant with milky-veined leaves and which exudes a milky liquid from the hollow stems (when cut).
So called for two compounding reasons: the leaves have milky white veins, not unlike the leaves of some garden varieties of Rare Lords-and-Ladies and, when cut or damaged, the sap which oozes out is milky white.
Milk Thistle likes sparsely grassy ground and waysides, especially near the coast. It prefers South Eastern parts of the UK but is to be found in various places as far north as Inverness and as far west as Truro. In Ireland it is scattered and seems to be in decline, there being only two hectads where it was reported in the 2000-2009 decade, plus a new Hectad for > 2010. The above example, the photographer Paula O'Meara reports, is the first to be recorded in Ireland in 2010, and the only one found in Co. Wexford for 15 years.
In the UK, there is only one plant in the Silybum Genus, but elsewhere a second member exists: Silybum eburneum variously called Silver Milk Thistle, Elephant Thistle and Ovary Thistle. Various other plants which were once included within the Genus Silybum, have since - on closer inspection, been moved into other Genera.
In autumn and after flowering, the straw-coloured dried thistle heads can take on a resemblance to spent Carline Thistle heads, but that is a much shorter plant.
The milky sap of Milk Thistle contains a mixture of substances called collectively Silimarin.
Silimarin, an anti-hepatotoxic, consists of a number of
flavonolignans based upon the
flavonol Taxifolin, which itself is one of the (minor) constituents of Silimarin. Taxifolin is also found in
Siberian Larch, False Acacia and in
Chinese Yew (Taxus chinensis var. mairei) from which it derived its name and in small amounts in Red Onions. Chemically, Taxifolin is
dihydroquercetin but compared to Quercetin, another flavonol, Taxifolin has low toxicity. Taxifolin seems to be effective against breast cancer cells and skin fibroblasts.
The major active component of Silimarin is
Silibinin (aka Silibin), a flavonolignan and
benzodioxane, which occurs as a mixture of both
Silibinin A and
Silibinin B, which are
stereoisomers) of one another. Silibinin accounts for 50% to 70% of the constituents of Silimarin. Silibinin is also an anti-oxidant. Additionally it exhibits anti-microbial activity towards Gram(-) bacteria or fungi, whereby it inhibits RNA and protein synthesis in these organisms (but not in Gram(+) bacteria). [Silimarin should not be confused with 'Silmarillion', the title of a fiction book by J.R.R. Tolkein and the follow-on from 'Lord of the Rings']
flavonolignan which occurs in Silimarin is
Isosilibinin, an isomer of Silibinin. [The portions of the molecules depicted in red have been inverted between the two]. Isosilybinin itself occurs in Simimarin as a mixture of two enantiomers,
Isosilibinin A and
Related to both Silibinin and Isosilybinin are two more flavonolignan constituents of
Silidianin, the two of which possess a 5-membered furan ring, whilst some other constituent moieties of Silibin have been shuffled around a bit [shown in green].
The major difference between
Silidianin is not only the rearrangement of the groups shown in dark blue and green, but also the addition of a poly-cyclic component shown in light blue in a 3-D structure (shown below), with two interfused six-membered rings.
Silimarin also contains several other minor constituents:
Silhermin, Neosili Hermins A and B, 2,3-dehydroSilibinin, 2,3-dehydroSilicristin plus trimers, tetramers and pentamers of Silibinin (
The extract 'Silimarin' from sap of Milk Thistle has been used therapeutically for some time to treat chronic liver disease and to protect the liver from damage against toxins such as resulting from chemical intoxification, alcohol abuse or viral infections. Silimarin itself has but low toxicity. Silibinin has been shown to protect the liver from damage caused by the vapours from toxic chemicals such as the solvents
toluene, which can also enter the body through the skin. It may also reduce the effects of liver damage resulting from chemotherapy (a cancer treatment). Silibin has also been shown to be effective (together with other treatments such as hyperbaric oxygen and penicillin treatment) in
Death Cap (Amanita phalloides) mushroom poisoning, reducing the severity of the liver damage but, however, offers little protection for the kidneys from the mushroom toxins
Phalloidin. Silibinin accomplishes this feat by reactivating protein synthesis in the liver that is normally blocked by the mushroom toxins. It may also be useful as a lotion applied to the skin to treat skin cancers such as malignant melanoma and reduce insulin resistance in type II diabetics.
A commercial drug based upon Silibinin is called Legalon SIL and is the Disodium salt of Silibinin dihydrogen dihemiSuccinate. This is also used to treat intoxications by hepatotoxic substances including alcohol and the consumption of
Death Cap Mushrooms. The black and red moieties together are Silibin; the two blue moieties are the sodium salts of DiHydrogen Succinate additions. When Silibinin is given in combination with penicillin in treatment of toxic Amanita mushroom poisoning, the death rate halves from that of using penicillin alone. That is, 90% survive when treated with Silibinin and penicillin as opposed to only 80% with penicillin alone. The drug Legalon carries the Silibinin moiety transporting it more readily. The Silibinin first arrests then reverses the liver damage from Amanita poisoning. It is thus also used to treat chronic hepatitis and cirrhosis of the liver.
Preparations of Silimarin with β-Cyclodextrin is far more soluble than the Milk Thistle mixture Silimarin itself, and the Glycosides of Silibin exhibit better water solubility and an even stronger hepatoprotective effect.
Silimarin, the Milk thistle composite, is poisonous and has an LD50 in mice of 1.6g/kg. It can also give an allergic reaction in humans who are also sensitive to Ragweed,
Marigold, Daisy or
Chrysanthemum and other plants in the Asteraceae family.
It is a biennial herb growing up to 2m in height and is cultivated for the above pharmaceuticals it produces. It is also said to have the sharpest thorns of any thistle.