Silybum marianum

Silybum marianum is a species of thistle. It has various common names including milk thistle, blessed milkthistle, Marian thistle, Mary thistle, Saint Mary's thistle, Mediterranean milk thistle, variegated thistle and Scotch thistle (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. Once native from Southern Europe through Asia, it has spread throughout the world.

Description

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Milk thistle is an upright herb that can grow to be tall and has an overall conical shape. The largest specimens have hollow stems.

The leaves are oblong to lanceolate and long and typically pinnately lobed, with spiny edges like most thistles.

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.

Distribution and habitat

Silybum marianum is native from around the Mediterranean and much of Europe to Central Asia and India; in Africa it reaches as far south as Ethiopia. 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, and Colombia where it is considered an invasive weed. It also spreads invasively in almost all of Europe as a consequence of field cultivation.

Silybum marianum establishes itself in sunny, warm ruderal meadows in regularly disturbed places such as rubble deposits, at the foot of south-exposed walls or villages and on urban fallow land or on cattle pastures. However, it does not prefer dry, stony soils.

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

Cultivation

Milk thistle is an adaptive crop with low requirements. It is mainly cultivated as a medicinal plant but it is also sometimes used as a food source. It's mainly cultivated in Europe but also in Asia and North America. Milk thistle is a biennial plant, it is normally grown as an annual plant, which simplifies cultivation. When the main requirements of the plant are met, then the milk thistle will blossom in the first year.

Chemistry

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Traditional milk thistle extract is made from the seeds (technically the whole fruit), 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. In the water-soaked fruit, 41% of the mass is of the pericarp and 52% the mass is of the kernel (actual seed). Almost all of the flavolignan content is found in the pericarp.

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). More complete extraction of flavonolignans from the fruit is a topic of ongoing research.

Toxicity

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.

Use of milk thistle may cause stomach upset and produce allergic reactions in some people. Eyelid edema, ocular pruritus, dry eye, diplopia, and blurred vision are among the reported complications based on registered side effects in the WHO global database of adverse drug reactions.

Leaf toxicity

Because of nitrate

Uses

Although potentially allergenic, the leaves and stems can be gathered ahead of bloom, the spines removed, and boiled with salt. The roots are edible raw or roasted and the flower head can be cooked like globe artichoke. 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."

Silymarin is extracted from the milk thistle seeds (technically the fruits) and available as a standardized extract. In 2018, the European Medicines Agency published an assessment report on the oral use of milk thistle fruit and its extracts in EU states. It finds that there is a "well-established use" of hepatoprotection approved by 11 countries and a "traditional use" of dyspeptic complaints in 4 countries. EMA has also published a monograph on this herbal substance.

Gallery

File:Silybum marianum Briones 3.jpg|Silybum marianum at Briones Regional Park.

File:Silybum marianum Briones 2.jpg|Growing in a field

File:Silybum marianum Gaertn. JdP.jpg|Detail of the foliage

File:Milk thistle flowerhead.jpg|Detail of the flower

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