Centaurea maculosa
Encyclopedia
Centaurea maculosa, the spotted knapweed, is a species of Centaurea
native to eastern Europe
.
It has been introduced to North America
, where it is considered an invasive plant species
in much of the western United States and Canada. In 2000, C. maculosa occupied more than 7 million acres (28,328 km²) in the US.
Knapweed is a pioneer species
found in recently disturbed sites or openings. Once it has been established at a disturbed site, it continues to spread into the surrounding habitat. This species outcompetes natives through at least three methods:
Its seed is an achene
about a quarter of an inch long with a small bristly pappus
at the tip which makes the wind its primary means of dispersal
. The leaves are a pale grayish-green. They are covered in fine short hairs. The lower leaves arrange a basal rosette, alternate, up to 6 inches (152.4 mm) long, deeply divided into lobes. Stem leaves less lobed progressively getting smaller toward the top. The stem is erect or ascending, slender, hairy and branching, which can grow up to three feet tall.
agents have been used against this plant and its cogener, diffuse knapweed
, including the moth
s Agapeta zoegana
and Metzneria paucipunctella
, the weevil
s Bangasternus fausti
, Larinus obtusus
, and Larinus minutus
and Cyphocleonus achates
, and the fruit flies
Chaetorellia acrolophi
, Urophora affinis
and Urophora quadrifasciata. But in general, biocontrol has not been shown to be effective against C. maculosa . In some instances, root-herbivory on C. maculosa stimulates additional release of catechin, the main allelopathic chemical which the species emits.
, It acts as an herbicide to inhibit competition by a wide range of other plant species. This phytotoxic compound inhibits seed germination and growth in making phosphorus
more available in certain soils. It leads to cell death of competing plants by acidification of the cytoplasm. Some natives, such as Gaillardia grandiflora and Lupinus sericeus
, are resistant to catechin-induced toxicity. This resistance is conferred by these plants' ability to produce oxalate
. Furthermore, native grasses grown in conjunction with oxalate-producing plants benefited from presence of oxalate.
Centaurea
Centaurea is a genus of between 350 and 600 species of herbaceous thistle-like flowering plants in the family Asteraceae. Members of the genus are found only north of the equator, mostly in the Eastern Hemisphere; the Middle East and surrounding regions are particularly species-rich...
native to eastern Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
.
It has been introduced to North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
, where it is considered an invasive plant species
Invasive species
"Invasive species", or invasive exotics, is a nomenclature term and categorization phrase used for flora and fauna, and for specific restoration-preservation processes in native habitats, with several definitions....
in much of the western United States and Canada. In 2000, C. maculosa occupied more than 7 million acres (28,328 km²) in the US.
Knapweed is a pioneer species
Pioneer species
Pioneer species are species which colonize previously uncolonized land, usually leading to ecological succession. They are the first organisms to start the chain of events leading to a livable biosphere or ecosystem...
found in recently disturbed sites or openings. Once it has been established at a disturbed site, it continues to spread into the surrounding habitat. This species outcompetes natives through at least three methods:
- A tap root that sucks up water faster than the root systems of its neighbors,
- Quick spread through high seed production, and
- Low palatability, meaning it is less likely to be chosen as food by herbivores. It is also suspected to be allelopathic, releasing a toxinToxinA toxin is a poisonous substance produced within living cells or organisms; man-made substances created by artificial processes are thus excluded...
from its roots that stunts the growth of nearby plants of other species.
Its seed is an achene
Achene
An achene is a type of simple dry fruit produced by many species of flowering plants. Achenes are monocarpellate and indehiscent...
about a quarter of an inch long with a small bristly pappus
Pappus (flower structure)
The pappus is the modified calyx, the part of an individual disk, ray or ligule floret surrounding the base of the corolla, in flower heads of the plant family Asteraceae. The pappus may be composed of bristles , awns, scales, or may be absent. In some species, the pappus is too small to see...
at the tip which makes the wind its primary means of dispersal
Biological dispersal
Biological dispersal refers to species movement away from an existing population or away from the parent organism. Through simply moving from one habitat patch to another, the dispersal of an individual has consequences not only for individual fitness, but also for population dynamics, population...
. The leaves are a pale grayish-green. They are covered in fine short hairs. The lower leaves arrange a basal rosette, alternate, up to 6 inches (152.4 mm) long, deeply divided into lobes. Stem leaves less lobed progressively getting smaller toward the top. The stem is erect or ascending, slender, hairy and branching, which can grow up to three feet tall.
Biocontrol
Thirteen biological pest controlBiological pest control
Biological control of pests in agriculture is a method of controlling pests that relies on predation, parasitism, herbivory, or other natural mechanisms...
agents have been used against this plant and its cogener, diffuse knapweed
Diffuse knapweed
Diffuse Knapweed , also known as White Knapweed or Tumble Knapweed, is a member of the genus Centaurea in the family Asteraceae. It is native to Asia Minor , the Balkans, , Ukraine, and southern Russia. Diffuse knapweed is an annual or biennial plant, generally growing to between 10 and 60 cm...
, including the moth
Moth
A moth is an insect closely related to the butterfly, both being of the order Lepidoptera. Moths form the majority of this order; there are thought to be 150,000 to 250,000 different species of moth , with thousands of species yet to be described...
s Agapeta zoegana
Agapeta zoegana
Agapeta zoegana is a species of moth known as the sulphur knapweed moth and the yellow-winged knapweed root moth. It is used as an agent of biological pest control against noxious knapweeds, particularly spotted knapweed and diffuse knapweed .The adult moth is bright yellow with areas of brown on...
and Metzneria paucipunctella
Metzneria paucipunctella
Metzneria paucipunctella is a species of moth known as the spotted knapweed seed head moth. It is used as an agent of biological pest control against noxious knapweeds, particularly spotted knapweed ....
, the weevil
Weevil
A weevil is any beetle from the Curculionoidea superfamily. They are usually small, less than , and herbivorous. There are over 60,000 species in several families, mostly in the family Curculionidae...
s Bangasternus fausti
Bangasternus fausti
Bangasternus fausti is a species of true weevil known as the broad-nosed seed head weevil. It is used as an agent of biological pest control against noxious knapweeds, particularly spotted knapweed , squarrose knapweed Bangasternus fausti is a species of true weevil known as the broad-nosed seed...
, Larinus obtusus
Larinus obtusus
Larinus obtusus is a species of true weevil known as the blunt knapweed flower weevil. It is used as an agent of biological pest control against noxious knapweeds, especially spotted knapweed ....
, and Larinus minutus
Larinus minutus
Larinus minutus is a species of true weevil known as the lesser knapweed flower weevil. It is used as an agent of biological pest control against noxious knapweeds, especially diffuse knapweed and spotted knapweed....
and Cyphocleonus achates
Cyphocleonus achates
Cyphocleonus achates is a species of true weevil known as the knapweed root weevil. It is native to southern Europe and the Mediterranean and is used as an agent of biological pest control against noxious knapweeds, especially spotted knapweed .-Life History:The adult weevil is dark gray and white...
, and the fruit flies
Tephritidae
Tephritidae is one of two fly families referred to as "fruit flies", the other family being Drosophilidae. Tephritidae does not include the biological model organisms of the genus Drosophila , which is often called the "common fruit fly". There are nearly 5,000 described species of tephritid...
Chaetorellia acrolophi
Chaetorellia acrolophi
Chaetorellia acrolophi is a species of tephritid fruit fly known as the knapweed peacock fly. It is used as an agent of biological pest control against noxious knapweeds, especially spotted knapweed ....
, Urophora affinis
Urophora affinis
Urophora affinis is a species of tephritid or fruit flies in the genus Urophora of the family Tephritidae. It has been released in the United States and Canada as a biocontrol agent to control spotted knapweed. U. affinis became established in Montana in 1973.-Life History:U. affinis is...
and Urophora quadrifasciata. But in general, biocontrol has not been shown to be effective against C. maculosa . In some instances, root-herbivory on C. maculosa stimulates additional release of catechin, the main allelopathic chemical which the species emits.
Allelopathy via catechin
C. maculosa roots exude a substance called (-)-catechin, another stereoisomer of catechinCatechin
Catechin is a natural phenol antioxidant plant secondary metabolite. The term catechins is also commonly used to refer to the related family of flavonoids and the subgroup flavan-3-ols ....
, It acts as an herbicide to inhibit competition by a wide range of other plant species. This phytotoxic compound inhibits seed germination and growth in making phosphorus
Phosphorus
Phosphorus is the chemical element that has the symbol P and atomic number 15. A multivalent nonmetal of the nitrogen group, phosphorus as a mineral is almost always present in its maximally oxidized state, as inorganic phosphate rocks...
more available in certain soils. It leads to cell death of competing plants by acidification of the cytoplasm. Some natives, such as Gaillardia grandiflora and Lupinus sericeus
Lupinus sericeus
Lupinus sericeus is a species of flowering plant in the legume family known by the common name silky lupine, or Pursh's silky lupine. It is native to western North America from British Columbia to Arizona and east to Alberta and Colorado....
, are resistant to catechin-induced toxicity. This resistance is conferred by these plants' ability to produce oxalate
Oxalate
Oxalate , is the dianion with formula C2O42− also written 22−. Either name is often used for derivatives, such as disodium oxalate, 2C2O42−, or an ester of oxalic acid Oxalate (IUPAC: ethanedioate), is the dianion with formula C2O42− also written (COO)22−. Either...
. Furthermore, native grasses grown in conjunction with oxalate-producing plants benefited from presence of oxalate.
External Links
- Species Profile- Spotted Knapweed (Centaurea stoebe), National Invasive Species Information Center, United States National Agricultural LibraryUnited States National Agricultural LibraryThe United States National Agricultural Library is one of the world's largest agricultural research libraries, and serves as a National Library of the United States and as the library of the United States Department of Agriculture...
. Lists general information and resources for spotted knapweed