What thistles are
Prickles can also occur all over the plant, and they protect it from herbivores. The spines vary considerably by species: Cirsium heterophyllum has very soft spines, while Cirsium spinosissimum is the opposite. Species adapted to dry environments are typically more spiny.
Genera called thistle
The word thistle is sometimes taken to mean precisely the plants of the tribe Cardueae, especially the genera Carduus, Cirsium and Onopordum. Plants outside this tribe are sometimes also called thistles. Musk thistle is a name in the genus Carduus, star thistle in Centaurea, globe thistle in Echinops and cotton thistle in Onopordum. Some plants in other families are also called thistle, such as the Russian thistle (Salsola). Teasel is a different plant from thistle: it is the genus Dipsacus, in the family Caprifoliaceae.
Cirsium is a genus of perennial and biennial flowering plants in the Asteraceae. They are more precisely known as plume thistles. Cirsium differs from Carduus, Silybum and Onopordum in having achenes with a pappus of feathered hairs. The other genera have a pappus of simple unbranched hairs. Cirsium is the Greek word for thistle, kirsos, likely derived from 'swollen vein'.
Onopordum acanthium is the cotton thistle or Scotch thistle, a flowering plant in the family Asteraceae. The cotton thistle is native to Europe and Western Asia, from the Iberian Peninsula east to Kazakhstan. It is a vigorous biennial plant with coarse, spiny leaves and conspicuous spiny-winged stems. Cirsium vulgare, the spear thistle, is also known as Scotch or Scottish thistle and is the national flower of Scotland.
Uses
Certain species of Cirsium, such as Cirsium monspessulanum, Cirsium pyrenaicum and Cirsium vulgare, have traditionally been used as food in rural areas of southern Europe. Cirsium setidens is used as a vegetable in Korean cuisine. The genus Cynara includes the commercially important species of artichoke. Some species regarded as major weeds are sources of vegetable rennet used in commercial cheese making.
Some species of Silybum that occur as weeds are cultivated for seeds that yield vegetable oil and pharmaceutical compounds such as silibinin. Traditional milk thistle extract is made from the seeds, which contain approximately 4-6% silymarin. Silymarin is a complex mixture of polyphenolic molecules. There is no clinical evidence that milk thistle has any medicinal effect as of the year 2020.
Ecology
Biennial thistles are particularly noteworthy for their high wildlife value, producing copious floral resources for pollinators. Thistles and thistle-seed feeders provide important sustenance for goldfinches. Many thistles are troublesome weeds, including some invasive species of Cirsium, Carduus, Silybum and Onopordum.
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Related: Alpha Pinene · Angelica · Angelica Root · Angelica Root Oil · Artemisia · Barrenwort · Beachheather · Behini Tree
