Common Name: Spotted Knapweed (Knap is derived from the Anglo-Saxon word cnaep, meaning top, knob or button and refers to the flower bud, which is round and hard like a button; spotted refers to the black-tipped bracts at the base of the flower).

Scientific Name: Centaurea maculosa (The generic name refers to the centaur, a mythological creature that was half man and half horse; macula is Latin for spot).


Spotted Knapweed is native to the southeastern Mediterranean area, where many weeds are thought to have originated. It is the epitome of a weed in that it is an unwanted and uncultivated plant that grows to profusion at the expense of native species.  It is believed to have been introduced to North America from Eastern Europe in the early 20th century by being inadvertently mixed in with seeds used for agricultural production.  Starting from somewhere in the Great Plains of Southern Canada and the North Central United States, it has spread like a cancer  to cover several million acres of grazing land.


The success of C. maculosa as a plant (which imparts its pejorative weed designation) is attributable to a number of factors.  It is a prolific seed producer. A single seed plant can have up to 16 seed heads each with a score or more of seeds, all of which drop within a radius of one meter.  Field testing has shown that heavily infested fields can have seed densities of up to 40,000 seeds per square meter.  The plant is a perennial and lives on average three to five years and as long as nine years. It has long taproots that extend deep into the ground, thriving in locations that are too dry for other plants. It exudes an herbicide that permeates the soil to the detriment of other plants, which are thereby eliminated as competitors. As it is not a native species, it has no natural enemies in North America. It is therefore the penultimate pioneer plant, rapidly becoming established in disturbed areas, such as when wheeled vehicles are used on rangeland


Spotted Knapweed imparts a significant economic impact on rangeland.  It crowds out the native grasses that are used for forage by livestock, thereby decreasing available acreage.  Animals find the plant unpleasant to eat due to the sharp spines and the high fiber that is difficult to digest. However, when fields are infested to the extent that alternatives are limited, it suffices as forage.  It can be toxic, especially to horses.  A 1979 report estimated that the economic loss to ranchers was 80 cents per acre of knapweed infested pasturage. A 1984 study estimated that 800,000 hectares (about 2 million acres) of rangeland in Montana were contaminated which resulted in an annual operating loss of $4.5 Million. Indirect costs, such as reduced buying power of large ranchers, are estimated to range as high as $28 Million.  In the book "Collapse," Jared Diamond estimates the direct economic damage to Montana as $100 Million, noting that they are "a huge pain in the neck to farmers, as they cannot be controlled by any single measure."


Controlling Spotted Knapweed with agricultural chemicals costs about 15 dollars per acre. This far exceeds the revenue that can be generated from an acre of rangeland.  Because of this, the US Department of Agriculture joined the battle against knapweed in 1985.  A coordinated control program was initiated that took advantage of natural knapweed biological predators from Europe.  Of the 38 species of insects known to be associated with Spotted Knapweed, 12 have been approved and released in the United States.  Each of the 12 was field tested for possible damage to other plants, particularly those of economic importance such as sunflowers, safflowers and artichokes.  Most field work has been to spread the seed-head fly (Urohora affinis) whose eggs are laid on the flower head. When the eggs hatch, galls form around the larvae that prevent the formation of about 75 percent of the seeds. One major problem with this technique is that the fly does not have the biologic mobility of knapweed. Hence, designated individuals called collectors must gather infested knapweed and distribute it to new locations.


Spotted Knapweed is one of many plants of the genus Centaurea that constitute one of the largest plant groups in Southern Europe. These include the cornflower (because it grows wild in corn fields), the hurt sickle (because its stem is so tough that it will dull a farmer's sickle), and the bachelor's button (because it is well suited to adorning a courting males otherwise drab shirtfront).  The genus name is derived from the centaur Chiron of Greek Mythology. The centaurs were a race of half men, half horse that were noted for their cruel and lecherous behavior. It is probable that centaur, which is etymologically similar in Greek to "those who round up bulls," derives from a primitive population of cowmen of Thessaly who were also known for their boorishness.  Chiron, however, was an exception.  Educated by Artemis and Apollo, he became a teacher of many heroes, such as Achilles. He was wounded by a poisoned arrow shot by Hercules. As the wound could not be cured, he gave his immortality to Prometheus, an act for which Zeus placed him in the stars as part of the constellation Sagittarius. Chiron is credited with teaching mankind about the healing power of herbs, and is hence recognized by the generic name.

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