THISTLE, a composite plant of the genera Carduus, Cirsium, Centaurea, Onopordon or Sonchus. Other related plants are the golden thistle or Spanish oyster-plant (Scolymus his panicus) whose roots are used as a vegetable like salsify and parsnip, which they resemble somewhat closely in flavor; globe-thistles (Echinops), often planted in shrubberies and herbaceous borders for their striking effects; blessed thistle (Cnicus benedictus) a hardy an nual herb useful for rockeries and wild gar dens, but commonly regarded as a weed in the Mediterranean region where it is native, and in California where it has escaped cultivation; and the milk-thistle, also called blessed or holy thistle (see SILYBU M ) , of ten grown in European gardens for its edible roots, leaves and heads and also for its ornamental qualities. Several plants of other families have sometimes been called thistle from their apparent resemblance to true thistles. The best known of these are probably the blue thistle (Echium vulgare) of the Boraginacece, and the fuller's or clothier's teasel (Dipsacus fullonum) and its few related species of the family Dipsacacece.
Among the best known genera the following species are probably most widely recognized. The Scotch or cotton thistle (Onopordon acanthium) is a biennial occasionally grown in America and sometimes seen wild in the East ern States. It has cottony white spiny foliage and large solitary terminal heads of pale purple flowers. The plants are often six feet tall and are planted in front of dark colored shrubbery. They seem unlikely to prove troublesome as weeds in America. Some of its other popular names are Queen Mary's, silver, Argentine, oat, asses' and down thistle. The Scottish emblem
seems more likely to be really the stemless this tle (Cirsium acaule) which is common in Scot land. The so-called Canada thistle (Cirsium arvense) is a native of Europe. It has become a troublesome weed in fields where methods of cultivation and rotation are faulty, spreading both by its seeds and its perennial creeping root-stocks, every fragment of which is capable of propagating a new plant. ,Prevention of leaf formation by persistent cultivation is a sure remedy as well as a safeguard. The plant is a slender herb about three feet tall and has numerous small purplish pink flower heads. The bull thistle (C. lanceolatum) and the yellow thistle (C. horridulum) are also well-known relatives found along roadsides and in fields, especially pastures. The pasture thistle (Cir sium odoratum) is found in similar places. The star thistle (Cestaurea calcitrapa, etc.) bears a resemblance to the blessed thistle. Several related species, notably the corn flower, blue bottle, bachelor's button or bluet (C. cyanus) and the dusty miller (C. cinercirta) are popular garden plants. Three species of sow thistles— the common (Sonchus oleraceus), the field (S. arvensis) and the spiny leaved (S. asper) — are well-known weeds in the United States and the Carline thistle (Cortina vulgaris) plays a similar role upon poor soils in Europe. The last was so named because tradi tion says that Charlemagne used its roots medicinally.