Centaurea jacea (Brown Knapweed)

Overview

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Brown knapweed. <em>Centaurea jacea</em>

Interesting Facts

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Brown knapweed is listed as a noxious weed in Washington. [source]

Common Names

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Click on the language to view common names.

Common Names in English:

Brown Knapweed, Brown Starthistle, Brown-Ray Knapweed, Brownray Knapweed, Brownray Knapweed Centaurea Jacea

Common Names in French:

Centaurée Jacée, Jacée, Jacée Des Prés

Common Names in German:

Wiesen-Flockenblume

Description

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Family Compositae

The largest family of flowering plants , the Compositae (Asteraceae), comprising about 1,100 genera and more than 20,000 species and characterized by many small flowers arranged in a head looking like a single flower and subtended by an involucre of bracts. A head may consist of both ray flowers and disk flowers, as in the sunflower, of disk flowers only, as in the burdock, or of ray flowers only, as in the dandelion.

Genus Centaurea

Annuals , biennials, or perennials, 20-300 cm, glabrous or tomentose . Stems erect , ascending , or spreading , simple or branched. Leaves basal and cauline; petiolate or sessile; proximal blade margins often ± deeply lobed , (spiny in C. benedicta ), distal ± smaller, often entire, faces glabrous or ± tomentose, sometimes also villous , strigose , or puberulent , often glandular-punctate. Heads discoid , disciform , or radiant, borne singly or in corymbiform arrays. Involucres cylindric or ovoid to hemispheric . Phyllaries many in 6-many series, unequal, proximal part appressed , body margins entire. distal parts expanded into erect to spreading, usually ± dentate or fringed , linear to ovate appendages , spine. tipped or spineless. Receptacles flat, epaleate, bristly . Florets 10-many; outer usually sterile , corollas slender and inconspicuous to much expanded, ± bilateral ; inner fertile , corollas white to blue, pink, purple, or yellow, bilateral or radial , often bent at junction of tubes and throats , lobes linear-oblong, acute; anther bases tailed , apical appendages oblong ; style branches: fused portions with minutely hairy nodes, distinct portions minute. Cypselae ± barrel-shaped, ± compressed , smooth or ribbed , apices entire (denticulate in C. benedicta ), glabrous or with fine, 1-celled hairs , attachment scar . lateral (with or without elaiosomes) ; pappi 0 or ± persistent , of 1-3 series of smooth or minutely barbed , stiff bristles or narrow scales . x = 8, 9, 10, 11, 12, 13, 15.

Species ca. 500: introduced ; Eurasia , n Africa, widely introduced worldwide.

Taxonomic limits of Centaurea have been controversial. The genus has great morphologic diversity , and studies have revealed much cytologic (e.g. , N. Garcia-Jacas et al. 1996) and palynologic (e.g., G. Wagenitz 1955) variation as well. During the nineteenth and twentieth centuries, various taxonomists attempted, with limited success, to divide Centaurea into smaller genera or workable infrageneric taxa. The relations of several satellite genera have been controversial as well.

Recent molecular phylogenetic studies (A. Susanna et al. 1995; N. Garcia-Jacas et al. 2000, 2001) have begun to clarify relationships within Centaurea and between Centaurea and other genera. These studies make it clear that Centaurea as traditionally defined is polyphyletic, and that generic boundaries should be realigned if monophyletic taxa are to be recognized. Some taxa traditionally included within Centaurea (e.g., the two native North American species, Centaurea americana and C. rothrockii) fall outside the redefined generic boundaries and are here treated in Plectocephalus. Others usually placed into segregate genera (e.g., Cnicus benedictus) are firmly nested within Centaurea. Because the type species of Centaurea (C. centaurium Linnaeus, an African species) falls outside the main lineage of the genus, a proposal has been made to conserve Centaurea with a different type species (W. Greuter et al. 2001), thereby maintaining the nomenclatural stability of most of the numerous species that do fall within the principal Centaurea clade.

Although several Centaurea species are widely established as members of the North American flora , and some of these are widely distributed invasive weeds , some of the taxa listed by J. T. Kartesz and C. A. Meacham (1999) are apparently waifs and not permanent members of the flora. These taxa are discussed informally immediately below.

Although Cnicus has usually been recognized as a distinctive monotypic genus, it has been merged into Centaurea by various authors (e.g., K . Bremer 1994; G. Wagenitz and F. H. Hellwig 1996) . Recent molecular systematic studies (N. Garcia-Jacas et al. 2000) provide additional evidence that it is nested within Centaurea.[1]

Physical Description

Species Centaurea jacea

Perennials , 30-150 cm. Stems 1-few, erect or ascending , openly branched distally, villous to scabrous with septate hairs , loosely tomentose , ± glabrate . Leaves: basal and proximal cauline petiolate , blades oblanceolate or elliptic , 5-25 cm, margins entire or shallowly dentate to irregularly pinnately lobed ; distal cauline sessile, not decurrent, gradually smaller, blades linear to lanceolate, entire or dentate. Heads radiant, in few-headed corymbiform arrays, leafy-bracted pedunculate . Involucres ovoid to campanulate or hemispheric , 15-l8 mm, usually about as wide as high. Principal phyllaries: bodies lanceolate to ovate , loosely tomentose or glabrous , usually concealed by expanded appendages , appendages usually light brown, erect, overlapping, ± concave , usually roundish, margins pale , broad, entire to coarsely dentate, membranous. Inner phyllaries: tips truncate , irregularly dentate or lobed. Florets 40-100+; corollas purple (rarely white), those of sterile florets ± expanded, exceeding corollas of fertile florets, those of fertile florets 15-18 mm. Cypselae tan, 2.5-3 mm, finely hairy ; pappi absent. 2n = 22, 44. [source]

The Centaurea jacea complex has been the subject of much controversy. The plants are widely distributed in Europe and variable in readily noticeable characters of the heads , florets, and cypselae. Several entities are commonly recognized, usually at the species level. The various named taxa are apparently all more or less interfertile , and natural hybridization has resulted in a plethora of intermediates that variously combine the features of the parental types. The numerous intermediates have been considered to be interspecific hybrids in some treatments or alternatively have been named as species or as infraspecific taxa within one or another of the parental species. The nomenclatural tangles are daunting, complicated by misapplication of names and the inadequate indexing of infraspecific names . [source]

In an elegant biosystematic study of the representatives of this complex in England, E. M. Marsden-Jones and W. B . Turrill (1954) demonstrated the hazards of attempting to apply different names to all of the numerous intermediates. Despite the clear evidence that the entities are part of one biological species , Marsden-Jones and Turrill chose, for nomenclatural convenience, to treat the English plants as three species (Centaurea jacea, C. nigra, and C. nemoralis) with numerous interspecific hybrids rather than as a single variable species, thereby leaving a large number of sexually reproducing forms unassignable to species. [source]

Further biosystematic studies of the Centaurea jacea complex involving additional races were carried out by C. Gardou (1972). She demonstrated that there are at least 18 diploid cytotypes within this complex plus a number of tetraploids . Most of the diploids have discrete geographic ranges in Europe. Some diploid members of the complex are apomictic, others autogamous , and still others outcrossers. Hybrids among the diploids are variably interfertile. Various tetraploids have arisen; some resemble one or another of the diploid races; many apparently allotetraploid races variously combine features of the diploids. The tetraploids of various origins are fully interfertile, have much wider ecologic tolerances than the diploids, and have spread widely. Introgression is common. Some of the diploids easily hybridize with tetraploids. The many intermediates are difficult to classify. Gardou's conclusion was that if one were strictly to apply the biological species concept, one would have to consider the complex, which she treated as sect. Jacea Cassini, to be a single species. Gardou did not, however, offer a taxonomic treatment of the complex that reflected her conclusion. [source]

J. Dostáls (1976) treatment of Centaurea for Flora Europaea represents an opposing approach, with numerous species recognized in the C. jacea complex and distributed into three sections within what he treated as subg. Jacea (Miller) Hayek. He further divided some of these species into subspecies . This typological approach may be useful in sorting the variable entities into convenient pigeonholes, but it artificially applied a semblance of order to an unruly complex of interbreeding races. [source]

North American botanists have usually recognized three or four species within the Centaurea jacea complex: C. jacea, C. nigra, C. nigrescens and/or C. dubia (under several different names), and C. ×pratensis, the last a collective for the various intermediates between C. jacea and C. nigra. According to G. Wagenitz (1987), the illegitimate name C. pratensis Thuillier refers to a dubious, ill-defined taxon of presumably hybrid origin that is also treated as C. thuillieri, C. debeauxii subsp. thuillieri, and as a subspecies of C. nigra. For spontaneous interspecific hybrids between C. jacea and C. nigra the name C. ×moncktonii C. E. Britton is accepted by C. A. Stace (1991) and in other recent European floras. The European sources of the North American plants have not been determined, and it is likely that multiple introductions have occurred. The taxon recognized as C. nemoralis Jordan by E. M. Marsden-Jones and W. B. Turrill (1954) has usually been included by American botanists in C. nigra (e.g. , R. J. Moore and C. Frankton 1974). Both diploid and tetraploid counts have been published from North American material . [source]

Neither E. M. Marsden-Jones and W. B. Turrill (1954) nor C. Gardou (1972) discussed the relationship of Centaurea nigrescens to C. jacea and C. nigra, though Gardou by implication included C. nigrescens in her conclusion that sect. Jacea is a single biological species. Centaurea nigrescens has been variously merged with C. jacea and C. nigra in past treatments or maintained as a distinct species, sometimes with multiple subspecies (e.g., J. DostÃ¡l 1976). H. A. Gleason and A. Cronquist (1991) and several other recent authors treated C. nigrescens as a synonym of C. dubia Suter. [source]

We have chosen here to follow the traditional approach for North American material of recognizing three species, Centaurea jacea, C. nigra, and C. nigrescens plus a nothospecies , C. ×moncktonii, though, as indicated above, these could as well be treated as a single species, C. jacea, comprising broadly inclusive subspecies. For those who prefer the latter approach, the respective names are Centaurea jacea subsp. jacea, C. jacea subsp. nigra (Linnaeus) Bonnier and Layens, and C. jacea subsp. nigrescens (Willdenow) Celakovsky. The hybrids between C. jacea and C. nigra may be treated as the nothosubspecies C. jacea subsp. ×pratensis (W. D. J. Koch) Celakovsky (as subsp.) ; the epithet pratensis is legitimate at the subspecific level. [source]

We do not attempt here to differentiate for North American material the various subspecies of Centaurea jacea that have been recognized in European floras (e.g., J. Dostál 1976). [source]

Habit: Forb/herb

Flowers: Bloom Period: May, June, July, August, September, October. • Flower Color: magenta

Size/Age/Growth

Size: 12-18" tall.

Habitat

Roadsides, fields , pastures, waste ground ; 50-1300 m.

Typically found at an altitude of 0 to 1,422 meters (0 to 4,665 feet).[2]

Biology

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Reproduction

Duration: Perennial

Growth

Culture: Space 18-24" apart.

Sunlight: Sun Exposure: Full Sun .

Temperature: Cold Hardiness: 6a. (map)

Taxonomy

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Domain: Eukaryota () - Whittaker & Margulis,1978 - eukaryotes
- Kingdom: Plantae () - Haeckel, 1866 - Plants
  - Subkingdom: Viridaeplantae () - Cavalier-Smith, 1981
    - Phylum: Tracheophyta () - Sinnott, 1935 ex Cavalier-Smith, 1998 - Vascular Plants
      - Subphylum: Euphyllophytina ()
        Class: Spermatopsida () - Brongniart, 1843
        Subclass: Asteridae () - Takhtajan, 1967
        Superorder: Campanulanae () - Takhtajan Ex Reveal, 1992
        Order: Asterales () - Lindley, 1833
        Family: Compositae () - Giseke, 1792, nom. cons., nom. alt.
        Subfamily: Carduoideae ()
        Tribe: Cardueae ()
        Subtribe: Centaureinae ()
        Genus: Centaurea () - C. Linnaeus, 1753 - Knapweed, star thistle, cornflower [Greek kentaurieon, ancient plant name associated with Chiron, a centaur famous for knowledge of medicinal plants]
        Specific epithet: jacea - L.
        Botanical name: - Centaurea jacea L.

Synonyms

Jacea pratensis Lamarck

Similar Species

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Members of the genus Centaurea

ZipcodeZoo has pages for 82 species, subspecies, varieties, forms, and cultivars in this genus:

More Info

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Notes

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Contributors

Brands, S.J. (comp.) 1989-present. The Taxonomicon. Universal Taxonomic Services, Zwaag, The Netherlands. Accessed March 27, 2012.

Data Sources

Accessed through GBIF Data Portal November 17, 2007:

Jyväskylä University Museum - The Section of Natural Sciences, Vascular plant collection of Jyvaskyla University Museum
Natural History Museum, University of Oslo, Vascular Plant Herbarium, Oslo
Natural History Museum, University of Oslo, Vascular Plants, Field notes, Oslo
Oregon State University, Vascular Plant Collection
The Danish Biodiversity Information Facility, Botany registration database by Danish botanists
The Swedish Museum of Natural History
, Botany
The Swedish Museum of Natural History
, Herbarium of Oskarshamn
The Swedish Museum of Natural History
, Lund Botanical Museum
The Swedish Museum of Natural History
, Plants
UK National Biodiversity Network, Botanical Society of the British Isles - Vascular Plants Database

Identifiers

Biodiversity Heritage Library NamebankID: 2658261
Catalogue of Life Accepted Name Code: Ast-1754
Global Biodiversity Information Facility Taxonkey: 3924291
Globally Unique Identifier: urn:lsid:ipni.org:names:56975-3
GRIN Nomen Number: 9821
Integrated Taxonomic Information System (ITIS) Taxonomic Serial Number (TSN): 36962
Natural Heritage Network Species Identifier: PDAST1Y0A0
U.S.D.A. Plant Symbol: CEJA
Zipcode Zoo Species Identifier: 27159

Footnotes

David J. Keil, Jörg Ochsmann "Centaurea". in Flora of North America Vol. 19, 20 and 21 Page 52, 57, 58, 67, 83, 84, 96, 171, 172, 176, 177, EFloras.org. [back]
Mean = 212.340 meters (696.654 feet), Standard Deviation = 277.140 based on 2,589 observations. Altitude information for each observation from British Oceanographic Data Centre. [back]

Centaurea jacea

Overview

Interesting Facts

Common Names

Description

Family Compositae

Genus Centaurea

Physical Description

Species Centaurea jacea

Size/Age/Growth

Habitat

Biology

Reproduction

Growth

Taxonomy

Synonyms

Similar Species

Members of the genus Centaurea

More Info

Further Reading

Notes

Contributors

Data Sources

Identifiers

Footnotes