The generic name, Cirsium, is derived from the classical Greek word for 'thistle'. The compilers of one nineteenth-century account of the world's plants dismissed the genus as not being of 'sufficient interest to require further attention'. During the twentieth century, the spear thistle came to have major negative economic effects on global livestock productivity.
Cirsium vulgare is one of the most common thistles in Britain and is typically found in meadows, field and road margins and waste ground where soil fertility is high. A native of Eurasia, its range extends from the Atlantic coast of Europe to the Pacific coast of China, and is closely linked to the distribution of cultivated land. Wherever Europeans have migrated, the spear thistle has been introduced in their wake, for example, to Colonial North America and nineteenth-century temperate South America and Australasia.
Spear thistles are usually biennial, producing a rosette of leaves with a deep taproot during their first year of growth following seed germination. Flowering happens in the second year; the plant then dies. Spear thistles may reach three metres in height with spiny leaves up to 30 centimetres long. Lilac-purple flower heads are produced in mid-summer; up to 200 fruits may form in each flower head. There are reports of individual plants producing over 50,000 fruits.
Spear thistle fruits have white, feathery hairs (pappus) attached to them to aid wind dispersal. However, the fruits are not dispersed by wind over long distances; the pappus is readily detached. In late summer pappi are often seen floating in the air; they are sometimes called 'sugar stealers'. Fruits are effectively dispersed by animals such as birds and as contaminants of animal fodder.
Despite the numbers of fruits a single plant produces, herbivory of flowering stems and predation by animals of the oil-rich seed means few spear thistle seedlings survive to maturity. The fruits survive about five years in the seed bank but most germinate soon after release from the parent plant.
In much of its native and introduced areas the spear thistle is an invasive species that reduces the productivity of pasture land, and costs tens of millions of pounds to control each year. In Britain the spear thistle is one of only five species covered by the 1959 Weeds Act.
Spear thistle fruits produce high-quality edible oil, whilst immature flower heads and young stalks have been eaten in a similar way to globe artichokes.
Forcella F and Randall JM 1994. Biology of bull thistle, Cirsium vulgare (Savi) Tenore. Reviews of Weed Science 6: 29-50.
Klinkhamer PGL and de Jong TJ 1993. Biological Flora of the British Isles, No. 176. Cirsium vulgare (Savi) Ten. Journal of Ecology 81: 177-191.
Klinkhamer PGL et al. 1988. Production, dispersal and predation of seeds in the biennial Cirsium vulgare. Journal of Ecology 76: 403-414.