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Centaurea diffusa

(Diffuse Knapweed)

Overview

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Interesting Facts

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Common Names

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Click on the language to view common names.

Common Names in English:

Diffuse Knapweed, Chaber Drobnogl, Diffuse Knaweed, Spreading Knapweed, Tumble Knapweed, White Knapweed, White Knapweed Centaurea Diffusa

Common Names in German:

Sparrige Flockenblume

Common Names in Portuguese:

Centáurea

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 diffusa

Annuals or perennials, 20-80 cm. Stems 1-several, much-branched throughout, puberulent and ± gray tomentose . Leaves hispidulous and ± short-tomentose; basal and proximal cauline petiolate , often absent at anthesis , blades 10-20 cm, margins bipinnately dissected into narrow lobes ; mid cauline sessile, bipinnately dissected; distal much smaller, entire or pinnately lobed . Heads disciform , in open paniculiform arrays. Involucres narrowly ovoid or cylindric , 10-13 × 3-5 mm. Principal phyllaries: bodies pale green, ovate to lanceolate, glabrous or finely tomentose, with a few prominent parallel veins, margins and erect appendages fringed with slender stramineous spines, each phyllary tipped by spine 1-3 mm. Inner phyllaries lanceolate, ± acute, appendage lacerate or spine-tipped. Florets 25-35; corollas cream white (rarely pink or pale purple), those of sterile florets 12-13 mm, slender, inconspicuous, those of fertile florets 12-13 mm. Cypselae dark brown, ca. 2-3 mm; pappi 0 or less than 0.5 mm, only rudimentary . 2n = 18, 36. Flowering summer (Jun-Aug). [source]

Centaurea diffusa readily hybridizes with C. stoebe subsp. micranthos and is often confused with their fertile hybrid (C. ×psammogena G. Gáyer) ; the latter can be recognized by its cypselae bearing pappi and having conspicuously radiant heads . Morphologically the hybrids are extremely variable; they may be intermediate or may closely resemble one or the other of the parents. Conspicuously radiant heads and pappi are always present; appendages of the phyllaries are brown to black, or rarely stramineous; spines are absent or short and 2n = 18. Centaurea ×psammogena is known from waste places, roadsides, railway tracks; 50-2500 m ; B .C., Ont., Que.; Colo., Mass., Mich., Mo., N.C., Oreg., Tenn., Wash . It may occur spontaneously where the ranges of the parent species overlap; they may also be distributed separately. In mixed stands it replaces C. diffusa by introgression. Hybrids are often misidentified as C. diffusa. [source]

Habit: Forb/herb

Flowers: Bloom Period: June, July, August. • Flower Color: mauve , near white, rose, white

Size/Age/Growth

Size: 12-18" tall.

Habitat

Disturbed sites in grasslands, woodlands, open coniferous forests ; 100-2200 m ; introduced ; Alta., B .C., Ont., Que., Sask., Yukon; Ariz., Calif., Colo., Conn., Idaho, Ill., Ind., Iowa, Ky., Mass., Mich., Mo., Mont., Nebr., Nev., N.H., N.J., N.Mex., Oreg., R.I., Tenn., Utah, Wash ., Wyo.; Europe. Centaurea diffusa is native to southeastern Europe and casually adventive in central and western Europe[2].

 

Typically found at an altitude of 0 to 2,998 meters (0 to 9,836 feet).[3]

Biology

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Reproduction

Duration: Annual , Perennial

Growth

Culture: Space 9-12" apart.

Soil: Minimum pH: 6.1 • Maximum pH: 7.5

Sunlight: Sun Exposure: Full Sun .

Moisture: Drought Tolerance: High

Temperature: Cold Hardiness: 3a, 3b, 4a, 4b, 5a, 5b, 6a, 6b, 7a, 7b, 8a, 8b, 9a, 9b, 10a. (map)

Taxonomy

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Synonyms

Acosta diffusa (Lam.) Soj�k • Acosta diffusa< /i> (Lam.) Soják

Notes

Name Status: Accepted Name .

Comment: Data Providers: New Zealand Plant Name Database, IPNI, Govaerts World Compositae Checklist A-G, Flora of China Checklist, Tropicos, Euro+Med. GCC LSID: urn :lsid:compositae.org:names:EA7532BD-4B03-480D-9A3A-00553B506E7F

Last scrutiny: 11-Aug-09

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:

C. akamantis (Akamas Centaury) · C. alpestris (Greater Centaury) · C. americana (American Basketflower) · C. americana 'Aloha' (American Knapweed) · C. americana 'Jolly Joker' (American Knapweed) · C. aspera (Rough Star-Thistle) · C. atropurpurea (Centaurea) · C. bella (Knapweed) · C. benoistii (Maroon Cornflower) · C. biebersteinii (Ballast Waif Centaurea Biebersteinii) · C. bovina (Pasture Knapweed) · C. cachinalensis (Flor Del Minero) · C. calcitrapa (Big-Head Purple Starthistle) · C. calcitrapoides (Smallhead Star-Thistle) · C. cineraria (Dusty Miller) · C. cineraria 'Colchester White' (Dusty Miller) · C. crupina (Crupina) · C. cyanoides 'Blue Carpet' (Cornflower) · C. cyanus (Bachelor's Button) · C. cyanus nana 'Jubilee Gem' (Bachelors Button) · C. cyanus 'Black Ball' (Bachelors Button) · C. cyanus 'Black Boy' (Bachelors Button) · C. cyanus 'Black Gem' (Bachelors Button) · C. cyanus 'Black Magic' (Bachelors Button) · C. cyanus 'Blue Boy' (Bachelors Button) · C. cyanus 'Blue Diadem' (Bachelors Button) · C. cyanus 'Classic Blue' (Bachelors Button) · C. cyanus 'Dwarf Blue Midget' (Bachelors Button) · C. cyanus 'Frosted Queen Mix' (Bachelors Button) · C. cyanus 'Frosty Mix' (Bachelors Button) · C. cyanus 'Mauve Queen' (Bachelors Button) · C. cyanus 'Polka Dot Mix' (Bachelors Button) · C. dealbata (Knapweed Centaurea Dealbata) · C. dealbata 'Rosea' (Knapweed) · C. debeauxii (Meadow Knapweed) · C. debeauxii thuillieri (Meadow Knapweed) · C. debeauxii subsp. thuillieri (Meadow Knapweed) · C. depressa (Centaurea) · C. diffusa (Diffuse Knapweed) · C. diluta (North African Knapweed) · C. eriophora (Sand-Heath) · C. gymnocarpa (Velvet Centaurea) · C. hypoleuca DC. 'John Coutts' (Knapweed) · C. iberica (Iberian Knapweed) · C. jacea (Brown Knapweed) · C. jacea x nigra (Hybrid Knapweed Centaurea Jacea X Nigra) · C. macrocephala (Armenian Basketflower) · C. melitensis (Cockspur Thistle) · C. moncktonii (Meadow Knapweed) · C. montana (Mountain Bluet) · C. montana 'Alba' (Mountain Bluet) · C. montana 'Amethyst in Snow' (Mountain Bluet) · C. montana 'Dot Purple' (Mountain Bluet) · C. montana 'Gold Bullion' (Batchelor's Button) · C. moschata 'Dairy Maid' (Sweet Sultan) · C. moschata 'Imperialis' (Sweet Sultan) · C. moschata 'The Bride' (Sweet Sultan) · C. nigra (Black Knapweed) · C. nigrescens (Short-Fringe Starthistle) · C. orientalis (Centaurea) · C. ovina (Lilac Knapweed) · C. paniculata (Jersey Knapweed) · C. phrygia (Scandinavian Starthistle) · C. pindicola (Centaurea) · C. pulcherrima (Pink Bachelors Button) · C. 'Pulchra Major' (Bachelor's Button) · C. ragusina (Dubrovacka Zecina) · C. rothrockii (Basket Flower) · C. scabiosa (Great Starthistle) · C. solstitialis (Barnaby Star-Thistle) · C. solstitialis solstitialis (St. Barnaby's Thistle) · C. stoebe (Spotted Knapweed) · C. sulphurea (Sicilian Starthistle) · C. thuillieri (Meadow Knapweed) · C. transalpina (Alpine Knapweed) · C. trichocephala (Feather-Head Knapweed) · C. triumfetti (Squarrose Knapweed Centaurea Triumfetti) · C. triumfettii (Spreading Thistle) · C. uniflora (Single-Flower Knapweed) · C. uniflora nervosa (Singleflower Knapweed) · C. xpratensis (Meadow Knapweed) · C.'Nigra' (Bachelor Buttons)

More Info

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Further Reading

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Notes

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Contributors

Data Sources

Accessed through GBIF Data Portal November 19, 2007:

Identifiers

Footnotes

  1. 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]
  2. "Centaurea diffusa". in Flora of North America Vol. 19, 20 and 21 Page 183, 190, 194. Oxford University Press. Online at EFloras.org. [back]
  3. Mean = 832.880 meters (2,732.546 feet), Standard Deviation = 731.070 based on 407 observations. Altitude information for each observation from British Oceanographic Data Centre. [back]
Last Revised: 7/14/2012