Silybum marianum

Daisy & Dandelion Family [Asteraceae]

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16th May 2014, Deganwy Castle, North Wales. Photo: © RWD
An alien spreading uncontrollably over the whole hillside; this is just one very small patch. Your Author can can see first hand that this plant is invasive, although it is the first time I have come across it.

14th Nov, 2010, Saltmills, Campile, Co. Wexford, Eire. Photo: © Paula O'Meara
A stout medium tall plant, growing up to 1m. This youngish specimen has yet to reach maturity and flower.

16th May 2014, Deganwy Castle, North Wales. Photo: © RWD
The spines are extremely sharp and long, it is not wise to fall on this plant. All the plants lower down the hill were getting ready to flower, but strangely only the plants atop the hill were actually already flowering.

14th Nov, 2010, Saltmills, Campile, Co. Wexford, Eire. Photo: © Paula O'Meara
Flower heads are solitary and up to 2 inches across. This flower has yet to open.

14th Nov, 2010, Saltmills, Campile, Co. Wexford, Eire. Photo: © Paula O'Meara
The lower part of the flower-head is covered in sharp narrow green phyllaries, which occur in several rows. The phyllaries have sharp spines especially nearer the flower-head.

16th May 2014, Deganwy Castle, North Wales. Photo: © RWD
The main stem is very stout, ribbed and upright.

16th May 2014, Deganwy Castle, North Wales. Photo: © RWD
Like most thistles it has a purplish flower head, but one which is larger than most other thistles. Note the wide ribbing on the main stem.

16th May 2014, Deganwy Castle, North Wales. Photo: © RWD
Which consists only of disc-florets.

16th May 2014, Deganwy Castle, North Wales. Photo: © RWD
Stems are ribbed, the ribs may be white.

16th May 2014, Deganwy Castle, North Wales. Photo: © RWD
A basal rosette of leaves on a new plant.

16th May 2014, Deganwy Castle, North Wales. Photo: © RWD
The leaves are typically thistle-like, but large, shiny green with sharp spines on the edges. The most notable feature are the milky white markings.

14th Nov, 2010, Saltmills, Campile, Co. Wexford, Eire. Photo: © Paula O'Meara
Milky white markings on the veins of the leaves. The edges are lobed and cusped and warped due to differential growth.

14th Nov, 2010, Saltmills, Campile, Co. Wexford, Eire. Photo: © Paula O'Meara
The leaves are a dark shiny, wet-looking waxy green. Sharp spines on the leaf-edge are yellow. Underside of leaf paler, less shiny, with short bristles.

No relation to : Purple Milk-Vetch, Alpine Milk-Vetch, Wild Milk-Vetch, Milk-parsley, 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 enantiomers (stereoisomers) of one another. Silibinin accounts for 50% to 70% of the constituents of Silimarin. Silibinin is also an anti-oxidant. It also exhibits anti-microbial activity towards Gram(-) bacteria or fungi, where it inhibits RNA and protein synthesis in these organisms, but not in Gram(+) bacteria.

Another 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 Isosilibinin B.

Related to both Silibinin and Isosilybinin are two more flavonolignan constituents of Silimarin: Silicristin and Silidianin, which both 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 Silicristin and 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: Silimonin, Isosilicristin, Silandrin, Silhermin, Neosili Hermins A and B, 2,3-dehydroSilibinin, 2,3-dehydroSilicristin plus trimers, tetramers and pentamers of Silibinin (Silibinomers).

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 xylene and 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 α-Amanitin and 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 for type II diabetics.

A commercial drug based upon Silibinin is called Legalon SIL and is Disodium Silibinin dihydrogen dihemisuccinate. This is also used to treat intoxications by hepatotoxic substances including alcohol and consumption of Death Cap Mushrooms.

It is a biennial herb growing up to 2m in height and is cultivated for the above pharmaceuticals it produces.

  Silybum marianum  ⇐ Global Aspect ⇒ Asteraceae  

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(Milk Thistle)


Silybum marianum

Daisy & Dandelion Family [Asteraceae]

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