''Silybum marianum'' is a species of

thistle Thistle is the common name of a group of flowering plants characterised by leaves with sharp prickles on the margins, mostly in the family Asteraceae. Prickles can also occur all over the planton the stem and on the flat parts of the leaves. ...

. It has various

common name In biology, a common name of a taxon or organism (also known as a vernacular name, English name, colloquial name, country name, popular name, or farmer's name) is a name that is based on the normal language of everyday life; and is often contrast ...

s including 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 ''Onopordum acanthium'' (cotton thistle, Scotch (or Scottish) thistle, not to be confused with ''Cirsium vulgare'' - spear thistle, which is also known as Scotch or Scottish thistle and is the national flower of Scotland. Spear thistle is nat ...

'' or ''

Cirsium vulgare ''Cirsium vulgare'', the spear thistle, bull thistle, or common thistle, is a species of the Asteraceae genus ''Cirsium'', native throughout most of Europe (north to 66°N, locally 68°N), Western Asia (east to the Yenisei Valley), and northwes ...

''). This species is an

annual Annual may refer to: *Annual publication, periodical publications appearing regularly once per year ** Yearbook ** Literary annual *Annual plant *Annual report *Annual giving *Annual, Morocco, a settlement in northeastern Morocco *Annuals (band), ...

biennial Biennial means (an event) lasting for two years or occurring every two years. The related term biennium is used in reference to a period of two years. In particular, it can refer to: * Biennial plant, a plant which blooms in its second year and th ...

plant of the family

Asteraceae The family Asteraceae, alternatively Compositae, consists of over 32,000 known species of flowering plants in over 1,900 genera within the order Asterales. Commonly referred to as the aster, daisy, composite, or sunflower family, Compositae w ...

. 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.

Description

Milk thistle is an upright herb that can grow to be tall and has an overall conical shape. The approximate maximum base diameter is . The stem is grooved and may be covered in a light cottony fuzz. The largest specimens have hollow stems. The leaves are oblong to lanceolate and 15–60 cm long and typically pinnately lobed, with spiny edges like most thistles. They are hairless, shiny green, with milk-white veins. 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

bract In botany, a bract is a modified or specialized leaf, especially one associated with a reproductive structure such as a flower, inflorescence axis or cone scale. Bracts are usually different from foliage leaves. They may be smaller, larger, or of ...

s which are hairless, with triangular, spine-edged appendages, tipped with a stout yellow spine. The fruits are black

achene An achene (; ), also sometimes called akene and occasionally achenium or achenocarp, is a type of simple dry fruit produced by many species of flowering plants. Achenes are monocarpellate (formed from one carpel) and indehiscent (they do not ope ...

s with a simple long white pappus, surrounded by a yellow basal ring. A long pappus acts as a "parachute", supporting seed dispersal by wind.

Distribution and habitat

''Silybum marianum'' is native to the

Mediterranean The Mediterranean Sea is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean Basin and almost completely enclosed by land: on the north by Western and Southern Europe and Anatolia, on the south by North Africa, and on the e ...

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 Hawaii ( ; haw, Hawaii or ) is a state in the Western United States, located in the Pacific Ocean about from the U.S. mainland. It is the only U.S. state outside North America, the only state that is an archipelago, and the only stat ...

Australia Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (continent), Australian continent, the island of Tasmania, and numerous List of islands of Australia, sma ...

New Zealand New Zealand ( mi, Aotearoa ) is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and over 700 smaller islands. It is the sixth-largest island count ...

Colombia Colombia (, ; ), officially the Republic of Colombia, is a country in South America with insular regions in North America—near Nicaragua's Caribbean coast—as well as in the Pacific Ocean. The Colombian mainland is bordered by the Car ...

where it is considered an invasive weed. Additionally, today it also spreads as invasive plant 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. The "giant thistle of the Pampas" reported by Darwin in the Voyage of the Beagle is thought by some to be ''Silybum marianum''.

Cultivation

Milk thistle is an adaptive crop with low requirements. It is mainly cultivated as a

medicinal plant Medicinal plants, also called medicinal herbs, have been discovered and used in traditional medicine practices since prehistoric times. Plants synthesize hundreds of chemical compounds for various functions, including Plant defense against her ...

but it's also mentioned as a food source.Karkanis, Anestis, Dimitrios Bilalis, und Aspasia Efthimiadou. „Cultivation of Milk Thistle (Silybum Marianum L. Gaertn.), a Medicinal Weed“. Industrial Crops and Products 34, Nr. 1 (1. Juli 2011): 825–30. https://doi.org/10.1016/j.indcrop.2011.03.027. It's mainly cultivated in

Europe Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a Continent#Subcontinents, subcontinent of Eurasia ...

but also in

Asia Asia (, ) is one of the world's most notable geographical regions, which is either considered a continent in its own right or a subcontinent of Eurasia, which shares the continental landmass of Afro-Eurasia with Africa. Asia covers an area ...

and

North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Car ...

. Milk thistle is a

biennial plant A biennial plant is a flowering plant that, generally in a temperate climate, takes two years to complete its biological life cycle. Life cycle In its first year, the biennal plant undergoes primary growth, during which its vegetative structures ...

, it is normally grown as a

annual plant An annual plant is a plant that completes its life cycle, from germination to the production of seeds, within one growing season, and then dies. The length of growing seasons and period in which they take place vary according to geographical ...

, which simplifies cultivation. This can be achieved when the main requirements are met, then the milk thistle already blossoms in the first year. Milk thistle has low soil requirements and is drought resistant. The optimal pH 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. For

germination Germination is the process by which an organism grows from a seed or spore. The term is applied to the sprouting of a seedling from a seed of an angiosperm or gymnosperm, the growth of a sporeling from a spore, such as the spores of fungi, fer ...

, 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 Fertilisation or fertilization (see spelling differences), also known as generative fertilisation, syngamy and impregnation, is the fusion of gametes to give rise to a new individual organism or offspring and initiate its development. Proce ...

is not necessarily needed because of the low nutrient requirements. A standard fertilization rate of 50 kg

nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...

, 30 kg

phosphorus Phosphorus is a chemical element with the symbol P and atomic number 15. Elemental phosphorus exists in two major forms, white phosphorus and red phosphorus, but because it is highly reactive, phosphorus is never found as a free element on Ear ...

and 60 kg

potassium Potassium is the chemical element with the symbol K (from Neo-Latin ''kalium'') and atomic number19. Potassium is a silvery-white metal that is soft enough to be cut with a knife with little force. Potassium metal reacts rapidly with atmosphe ...

per

hectare The hectare (; SI symbol: ha) is a non-SI metric unit of area equal to a square with 100-metre sides (1 hm2), or 10,000 m2, and is primarily used in the measurement of land. There are 100 hectares in one square kilometre. An acre is a ...

is applied before sowing, to improve yields. Harvest normally occurs in July or August. Since the flower heads don't ripen evenly, optimal harvest time is about a

fortnight A fortnight is a unit of time equal to 14 days (two weeks). The word derives from the Old English term , meaning "" (or "fourteen days," since the Anglo-Saxons counted by nights). Astronomy and tides In astronomy, a ''lunar fortnight'' is h ...

after 50% of the flower heads are dry. For harvesting a common

cereal A cereal is any Poaceae, grass cultivated for the edible components of its grain (botanically, a type of fruit called a caryopsis), composed of the endosperm, Cereal germ, germ, and bran. Cereal Grain, grain crops are grown in greater quantit ...

combine harvester The modern combine harvester, or simply combine, is a versatile machine designed to efficiently harvest a variety of grain crops. The name derives from its combining four separate harvesting operations—reaping, threshing, gathering, and winnow ...

can be used. In

Poland Poland, officially the Republic of Poland, is a country in Central Europe. It is divided into 16 administrative provinces called voivodeships, covering an area of . Poland has a population of over 38 million and is the fifth-most populous ...

, average yields are 1230 kg per ha with an average silmarin content of 26.5 kg per ha.

Chemistry

Traditional milk thistle extract is made from the seeds, which contain approximately 4–6%

silymarin Silibinin (International Nonproprietary Name, INN), also known as silybin (both from ''Silybum'', the Genus–differentia definition, generic name of the plant from which it is extracted), is the major active constituent of silymarin, a standard ...

. The extract consists of about 65–80% silymarin (a

flavonolignan Flavonolignans are natural phenols composed of a part flavonoid and a part phenylpropane. Examples Flavonolignans identified in ''Silybum marianum'' (milk thistle) silymarin complex include silibinin, silychristin, silydianin, dehydrosilybin, ...

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 Taxifolin (5,7,3',4'-flavan-on-ol), also known as dihydroquercetin, belongs to the subclass flavanonols in the flavonoids, which in turn is a class of polyphenols. Stereocenters Taxifolin has two stereocenters on the C-ring, as opposed to quer ...

Silibinin Silibinin ( INN), also known as silybin (both from ''Silybum'', the generic name of the plant Plants are predominantly photosynthetic eukaryotes of the kingdom Plantae. Historically, the plant kingdom encompassed all living things that ...

, 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 Traditional medicine (also known as indigenous medicine or folk medicine) comprises medical aspects of traditional knowledge that developed over generations within the folk beliefs of various societies, including indigenous peoples, before the ...

for centuries, there is no clinical evidence that it has any medicinal effect, and the quality of research has been poor. Silymarin is extracted from the milk thistle seeds and available as a standardized extract. In 2019,

Cancer Research UK Cancer Research UK (CRUK) is the world's largest independent cancer research organization. It is registered as a charity in the United Kingdom and Isle of Man, and was formed on 4 February 2002 by the merger of The Cancer Research Campaign and t ...

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." Use of milk thistle may cause stomach upset and produce

allergic reactions Allergies, also known as allergic diseases, refer a number of conditions caused by the hypersensitivity of the immune system to typically harmless substances in the environment. These diseases include hay fever, food allergies, atopic derma ...

in some people.

Toxicity

Milk thistle based supplements have been measured to have the highest

mycotoxin A mycotoxin (from the Greek μύκης , "fungus" and τοξίνη , "toxin") is a toxic secondary metabolite produced by organisms of kingdom Fungi and is capable of causing disease and death in both humans and other animals. The term 'mycotoxin' ...

concentrations of up to 37 mg/kg when compared to various plant-based dietary supplements.

Animal toxicity

Because of

nitrate Nitrate is a polyatomic ion A polyatomic ion, also known as a molecular ion, is a covalent bonded set of two or more atoms, or of a metal complex, that can be considered to behave as a single unit and that has a net charge that is not zer ...

content, the plant has been found to be toxic to cattle and sheep. When potassium nitrate is eaten by

ruminant Ruminants (suborder Ruminantia) are ungulate, hoofed herbivorous grazing or browsing mammals that are able to acquire nutrients from plant-based food by Enteric fermentation, fermenting it in a specialized stomach prior to digestion, principally ...

s, the bacteria in the animal's stomach breaks the chemical down, producing nitrite ions. Nitrite ions then combine with

hemoglobin Hemoglobin (haemoglobin BrE) (from the Greek word αἷμα, ''haîma'' 'blood' + Latin ''globus'' 'ball, sphere' + ''-in'') (), abbreviated Hb or Hgb, is the iron-containing oxygen-transport metalloprotein present in red blood cells (erythrocyte ...

to produce

methemoglobin Methemoglobin (British: methaemoglobin) (pronounced "met-hemoglobin") is a hemoglobin ''in the form of metalloprotein'', in which the iron in the heme group is in the Fe3+ (ferric) state, not the Fe2+ (ferrous) of normal hemoglobin. Sometimes, it i ...

, blocking the transport of oxygen. The result is a form of

oxygen deprivation Asphyxia or asphyxiation is a condition of deficient supply of oxygen to the body which arises from abnormal breathing. Asphyxia causes generalized hypoxia, which affects primarily the tissues and organs. There are many circumstances that can ...

.http://ucanr.edu/sites/UCCE_LR/files/180507.pdf Tucker JM, et al. Nitrate Poisoning in Livestock (1961)