''Centaurea macrocephala'' is a species of flowering plant in the family

Asteraceae The family Asteraceae, alternatively Compositae, consists of over 32,000 known species of flowering plants in over 1,900 genera within the order Asterales. Commonly referred to as the aster, daisy, composite, or sunflower family, Compositae w ...

, and a member of the thistle tribe, Cynareae. It has many common names, including bighead knapweed,''Centaurea macrocephala''.
USDA PLANTS. United States Department of Agriculture. big yellow centaurea,''Centaurea macrocephala''.
Integrated Taxonomic Information System (ITIS). lemon fluff,''Centaurea macrocephala''.
Invasive.org, Center for Invasive Species and Ecosystem Health. yellow bachelor's button,''Centaurea macrocephala''.
Flora of North America. eFloras.org yellow hardhat,''Centaurea macrocephala''.
Missouri Botanical Garden. and Armenian basketflower.''Centaurea macrocephala''.
Invasive Species Compendium. CABI. This plant is native to the

Caucasus The Caucasus () or Caucasia (), is a region between the Black Sea and the Caspian Sea, mainly comprising Armenia, Azerbaijan, Georgia, and parts of Southern Russia. The Caucasus Mountains, including the Greater Caucasus range, have historically ...

. It is known throughout much of the world as an

introduced species An introduced species, alien species, exotic species, adventive species, immigrant species, foreign species, non-indigenous species, or non-native species is a species living outside its native distributional range, but which has arrived there ...

and sometimes a

noxious weed A noxious weed, harmful weed or injurious weed is a weed that has been designated by an agricultural or other governing authority as a plant that is injurious to agricultural or horticultural crops, natural habitats or ecosystems, or humans or liv ...

. It is a popular garden plant, and is widely available for cultivation as an

ornamental Ornamental may refer to: *Ornamental grass, a type of grass grown as a decoration *Ornamental iron, mild steel that has been formed into decorative shapes, similar to wrought iron work *Ornamental plant, a plant that is grown for its ornamental qua ...

Description

This

herbaceous Herbaceous plants are vascular plants that have no persistent woody stems above ground. This broad category of plants includes many perennials, and nearly all annuals and biennials. Definitions of "herb" and "herbaceous" The fourth edition of t ...

perennial A perennial plant or simply perennial is a plant that lives more than two years. The term ('' per-'' + '' -ennial'', "through the years") is often used to differentiate a plant from shorter-lived annuals and biennials. The term is also wide ...

bears mostly unbranched stems reaching up to 170 cm tall. The leaves are variable in shape and size. Those near the base have oval blades borne on petioles and those higher on the plant have shorter, narrower blades. The flower heads are solitary atop the stems and have arrays of small leaves around the bases. The heads are 2.5 to 3.5 cm wide. The somewhat rounded head is covered in layers of phyllaries with fringed tips and sometimes spines. The head contains many yellow florets. The fruit, including its pappus, can be well over one centimeter long.

Biology

In its native range in the Caucasus, this plant grows in mountain meadows. It is a summer-flowering subalpine species. It thrives as an introduced species in many types of moist temperate habitat, especially areas dominated by perennial herbs. It can grow in disturbed areas.

Uses

This is a well-known ornamental flowering plant. It has been a garden flower for over 200 years, being introduced to the United Kingdom and United States in the early 19th century.

Thomas Jefferson Thomas Jefferson (April 13, 1743 – July 4, 1826) was an American statesman, diplomat, lawyer, architect, philosopher, and Founding Fathers of the United States, Founding Father who served as the third president of the United States from 18 ...

obtained seeds from the nurseryman Bernard McMahon and planted them at Monticello. In gardens it can be placed at borders or corners, where it will form clumps. It is used as a cut flower for its large, rounded heads with long yellow florets, and it can be used as a decorative dried flower. This is the largest '' Centaurea'' in cultivation and is easily recognized.

Ecology

As the plant has been transported around the world for ornamental use it has taken hold as an introduced species in several areas. It is a casual garden escapee in parts of Europe and North America. It has only become a troublesome

in a few areas, notably

Washington state Washington (), officially the State of Washington, is a state in the Pacific Northwest region of the Western United States. Named for George Washington—the first U.S. president—the state was formed from the western part of the Washington ...

in the United States, where it is prohibited to buy or sell the species. Its invasive nature is best seen in garden environments, where it is more aggressive than most other ornamental plants and can become a "garden thug".

Gallery

File:Centaurea macrocephala kz4.jpg, Form File:Centaurea macrocephala - Centaurée à grosse tête (2).jpg, Bud File:Centaurea macrocephala cropped-2832.jpg, Head File:Centaurea macrocephala (4998442941).jpg, Fringed brown phyllaries File:Centaurea macrocephala - 001x.jpg, Illustration

References

External links

* {{Taxonbar, from=Q1549425 macrocephala Plants described in 1803