''Silybum marianum'' is a species of

thistle Thistle is the common name of a group of flowering plants characterized by leaves with sharp spikes 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. T ...

. 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 con ...

s 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 ''Onopordum acanthium'' (cotton thistle, Scotch (or Scottish) thistle) is a flowering plant in the family Asteraceae. It is native to Europe and Western Asia from the Iberian Peninsula east to Kazakhstan, and north to central Scandinavia, and ...

'' or ''

Cirsium vulgare ''Cirsium vulgare'', commonly known as 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 ...

''). This species is an annual or

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 t ...

plant of the family

Asteraceae Asteraceae () is a large family (biology), family of flowering plants that consists of over 32,000 known species in over 1,900 genera within the Order (biology), order Asterales. The number of species in Asteraceae is rivaled only by the Orchi ...

. 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

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 A leaf (: leaves) is a principal appendage of the stem of a vascular plant, usually borne laterally above ground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", while the leaves, stem, ...

are oblong to lanceolate and long and typically

pinnately Pinnation (also called pennation) is the arrangement of feather-like or multi-divided features arising from both sides of a common axis. Pinnation occurs in biological morphology, in crystals, such as some forms of ice or metal crystals, and in ...

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. The flower head is surround by

bract In botany, a bract is a modified or specialized leaf, associated with a reproductive structure such as a flower, inflorescence axis or cone scale. Bracts are usually different from foliage leaves in size, color, shape or texture. They also lo ...

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 fruit, simple dry fruits, dry fruit produced by many species of flowering plants. Achenes are monocarpellate (formed from one carpel) and Dehi ...

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 Native may refer to: People * '' Jus sanguinis'', nationality by blood * '' Jus soli'', nationality by location of birth * Indigenous peoples, peoples with a set of specific rights based on their historical ties to a particular territory ** Nat ...

from around 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 east by the Levant in West Asia, on the north by Anatolia in West Asia and Southern ...

and much of Europe to

Central Asia Central Asia is a region of Asia consisting of Kazakhstan, Kyrgyzstan, Tajikistan, Turkmenistan, and Uzbekistan. The countries as a group are also colloquially referred to as the "-stans" as all have names ending with the Persian language, Pers ...

and

India India, officially the Republic of India, is a country in South Asia. It is the List of countries and dependencies by area, seventh-largest country by area; the List of countries by population (United Nations), most populous country since ...

; in Africa it reaches as far south as

Ethiopia Ethiopia, officially the Federal Democratic Republic of Ethiopia, is a landlocked country located in the Horn of Africa region of East Africa. It shares borders with Eritrea to the north, Djibouti to the northeast, Somalia to the east, Ken ...

. 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 ( ; ) is an island U.S. state, state of the United States, in the Pacific Ocean about southwest of the U.S. mainland. One of the two Non-contiguous United States, non-contiguous U.S. states (along with Alaska), it is the only sta ...

Australia Australia, officially the Commonwealth of Australia, is a country comprising mainland Australia, the mainland of the Australia (continent), Australian continent, the island of Tasmania and list of islands of Australia, numerous smaller isl ...

New Zealand New Zealand () is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and List of islands of New Zealand, over 600 smaller islands. It is the List of isla ...

, and

Colombia Colombia, officially the Republic of Colombia, is a country primarily located in South America with Insular region of Colombia, insular regions in North America. The Colombian mainland is bordered by the Caribbean Sea to the north, Venezuel ...

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 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 h ...

but it is also sometimes used 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 but also in Asia and North America. 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. Background In its first year, the biennial plant undergoes primary growth, during which its vegetative structur ...

, it is normally grown as an

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. Globally, 6% of all plant species and 15% of herbaceous plants (excluding trees and shrubs) are ...

, which simplifies cultivation. When the main requirements of the plant are met, then the milk thistle will blossom in the first year. Milk thistle has low soil nutrient 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, ...

, 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 American and British English spelling differences#-ise, -ize (-isation, -ization), spelling differences), also known as generative fertilisation, syngamy and impregnation, is the fusion of gametes to give ...

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

nitrogen Nitrogen is a chemical element; it has Symbol (chemistry), symbol N and atomic number 7. Nitrogen is a Nonmetal (chemistry), nonmetal and the lightest member of pnictogen, group 15 of the periodic table, often called the Pnictogen, pnictogens. ...

, 30 kg

phosphorus Phosphorus is a chemical element; it has Chemical symbol, symbol P and atomic number 15. All elemental forms of phosphorus are highly Reactivity (chemistry), reactive and are therefore never found in nature. They can nevertheless be prepared ar ...

and 60 kg

potassium Potassium is a chemical element; it has Symbol (chemistry), symbol K (from Neo-Latin ) and atomic number19. It is a silvery white metal that is soft enough to easily cut with a knife. Potassium metal reacts rapidly with atmospheric oxygen to ...

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), that is, square metres (), and is primarily used in the measurement of land. There are 100 hectares in one square kilometre. ...

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 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 hal ...

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

cereal A cereal is a grass cultivated for its edible grain. Cereals are the world's largest crops, and are therefore staple foods. They include rice, wheat, rye, oats, barley, millet, and maize ( Corn). Edible grains from other plant families, ...

combine harvester The modern combine harvester, also called a combine, is a machine designed to harvest a variety of cultivated seeds. Combine harvesters are one of the most economically important labour-saving inventions, significantly reducing the fraction of ...

can be used. In

Poland Poland, officially the Republic of Poland, is a country in Central Europe. It extends from the Baltic Sea in the north to the Sudetes and Carpathian Mountains in the south, bordered by Lithuania and Russia to the northeast, Belarus and Ukrai ...

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

Chemistry

Traditional milk thistle extract is made from the seeds, which contain approximately 4–6% silymarin. 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. It is extracted from plants such as Siberian larch and milk thistle. Stereocent ...

Silibinin Silibinin ( INN), also known as silybin (both from ''Silybum'', the generic name of the plant from which it is extracted), is the major active constituent of silymarin, a standardized extract of the milk thistle, containing a mixture of flav ...

, a semipurified fraction of silymarin, is primarily a mixture of 2

diastereoisomers In stereochemistry, diastereomers (sometimes called diastereoisomers) are a type of stereoisomer. Diastereomers are defined as non-mirror image, non-identical stereoisomers. Hence, they occur when two or more stereoisomers of a compound have dif ...

, silybin A and silybin B, in a roughly 1:1 ratio.

Toxicity

Milk thistle based supplements have been measured to have the highest

mycotoxin A mycotoxin (from the Greek μύκης , "fungus" and τοξικός , "poisonous") is a toxic secondary metabolite produced by fungi and is capable of causing disease and death in both humans and other animals. The term 'mycotoxin' is usually rese ...

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 Allergies, also known as allergic diseases, are various conditions caused by hypersensitivity of the immune system to typically harmless substances in the environment. These diseases include hay fever, food allergies, atopic dermatitis, alle ...

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 The World Health Organization (WHO) is a specialized agency of the United Nations which coordinates responses to international public health issues and emergencies. It is headquartered in Geneva, Switzerland, and has 6 regional offices and 15 ...

global database of adverse drug reactions.

Animal toxicity

Because of

nitrate Nitrate is a polyatomic ion with the chemical formula . salt (chemistry), Salts containing this ion are called nitrates. Nitrates are common components of fertilizers and explosives. Almost all inorganic nitrates are solubility, soluble in wa ...

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

ruminant Ruminants are herbivorous grazing or browsing artiodactyls belonging to the suborder Ruminantia that are able to acquire nutrients from plant-based food by fermenting it in a specialized stomach prior to digestion, principally through microb ...

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

hemoglobin Hemoglobin (haemoglobin, Hb or Hgb) is a protein containing iron that facilitates the transportation of oxygen in red blood cells. Almost all vertebrates contain hemoglobin, with the sole exception of the fish family Channichthyidae. Hemoglobin ...

to produce

methemoglobin Methemoglobin (British: methaemoglobin, shortened MetHb) (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 ...

, 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 all the tissues and organs, some more rapidly than others. There are ma ...

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 The artichoke (''Cynara cardunculus'' var. ''scolymus''),Rottenberg, A., and D. Zohary, 1996: "The wild ancestry of the cultivated artichoke." Genet. Res. Crop Evol. 43, 53–58. also known by the other names: French artichoke, globe artichoke, ...

. Although milk thistle has been used in

traditional medicine Traditional medicine (also known as indigenous medicine or folk medicine) refers to the knowledge, skills, and practices rooted in the cultural beliefs of various societies, especially Indigenous groups, used for maintaining health and treatin ...

for centuries, there is no clinical evidence that it has any medicinal effect as of the year 2020. 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 organisation. 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."