| Milk thistle | |
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Scientific classification | |
| Kingdom: | Plantae |
| Clade: | Tracheophytes |
| Clade: | Angiosperms |
| Clade: | Eudicots |
| Clade: | Asterids |
| Order: | Asterales |
| Family: | Asteraceae |
| Genus: | Silybum |
| Species: | S. marianum |
| Binomial name | |
| Silybum marianum (L.) Gaertn. | |
| Synonyms | |
Carduus marianusL. | |
Silybum marianum is a species ofthistle. It has variouscommon names includingmilk thistle,[2]blessed milkthistle,[3]Marian thistle,Mary thistle,Saint Mary's thistle,Mediterranean milk thistle,variegated thistle andScotch thistle (not to be confused withOnopordum acanthium orCirsium vulgare). This species is anannual orbiennial plant of the familyAsteraceae. 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.
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.[4] The approximate maximum base diameter is 160 cm (63 in). The stem is grooved and may be covered in a light cottony fuzz.[5] The largest specimens have hollow stems.
Theleaves are oblong to lanceolate and 15–60 cm (6–23+1⁄2 in) long and typicallypinnately lobed, with spiny edges like most thistles.[4] They are hairless, shiny green, with milk-white veins.[4]
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 theSouthern Hemisphere.[5] The flower head is surround bybracts which are hairless, with triangular, spine-edged appendages, tipped with a stout yellow spine.
The fruits are blackachenes with a simple long whitepappus, surrounded by a yellow basal ring.[6][4] A long pappus acts as a "parachute", supporting seed dispersal by wind.[7]
Silybum marianum isnative from around theMediterranean and much of Europe toCentral Asia andIndia; in Africa it reaches as far south asEthiopia.[8] It is possibly native near the coast of southeast England.S. marianum has been widelyintroduced outside its natural range, for example into North America,Hawaii,Australia,New Zealand, andColombia where it is considered aninvasive weed.[5][9][10] It also spreads invasively in almost all of Europe as a consequence of field cultivation.[11]
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.[11][12]
Milk thistle has been potentially observed to modify fire regimes in its invasive range.[13][14] Its invasion into new habitats may also be encouraged by fire.[15]
Milk thistle is an adaptive crop with low requirements. It is mainly cultivated as amedicinal plant but it is also sometimes used as a food source.[16][17] It's mainly cultivated in Europe but also in Asia and North America.[18] Milk thistle is abiennial plant, it is normally grown as anannual plant, which simplifies cultivation. When the main requirements of the plant are met, then the milk thistle will blossom in the first year.[16]
Milk thistle has low soil nutrient requirements and is drought resistant. The optimalpH ranges from 5.5 to 7.6, but a wide range is acceptable. The seeds are directly sown into the soil with a sowing depth of 1 to 1.5 cm. Forgermination, a minimal temperature of 2 °C is needed. Sowing can be done in Autumn or in Spring, depending on the climate conditions. Row spacing is between 40 and 75 cm with a plant space of about 25 cm in the rows.Fertilization is not necessarily needed because of the low nutrient requirements. A standard fertilization rate of 50 kgnitrogen, 30 kgphosphorus and 60 kgpotassium perhectare is applied before sowing, to improve yields. Harvest normally occurs in July or August. Since the flower heads do not ripen evenly, optimal harvest time is about afortnight after 50% of the flower heads are dry. For harvesting a commoncerealcombine harvester can be used. InPoland, average yields are 1230 kg per ha with an average silymarin content of 26.5 kg per ha.[19]
Traditional milk thistle extract is made from the seeds, which contain approximately 4–6%silymarin.[20] The extract consists of about 65–80% silymarin (aflavonolignan complex) and 20–35% fatty acids, including linoleic acid.[21] 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).[21]Silibinin, a semipurified fraction of silymarin, is primarily a mixture of 2diastereoisomers, silybin A and silybin B, in a roughly 1:1 ratio.[21][22]
Milk thistle based supplements have been measured to have the highestmycotoxin concentrations of up to 37 mg/kg when compared to various plant-based dietary supplements.[23]
Use of milk thistle may cause stomach upset and produceallergic reactions in some people.[24] Eyelid edema, ocular pruritus, dry eye, diplopia, and blurred vision are among the reported complications based on registered side effects in theWHO global database of adverse drug reactions.[25]
Because ofnitrate[5] content, the plant has been found to be toxic to cattle and sheep.[5] When potassium nitrate is eaten byruminants, the bacteria in the animal's stomach breaks the chemical down, producing nitrite ions. Nitrite ions then combine withhemoglobin to producemethemoglobin, blocking the transport of oxygen. The result is a form ofoxygen deprivation.[26]
Although potentially allergenic, the leaves and stems can be gathered ahead of bloom, the spines removed, and boiled with salt.[27] The roots are edible raw or roasted and the flower head can be cooked like globeartichoke.[27]
Although milk thistle has been used intraditional medicine for centuries, there is noclinical evidence that it has any medicinal effect as of the year 2020.[24][28][29] Silymarin is extracted from the milk thistle seeds and available as a standardized extract.[30] 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."[31]
The highest mycotoxin concentrations were found in milk thistle-based supplements (up to 37 mg/kg in the sum).
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