View source for Centaurea

{{Treatment/ID
|accepted_name=Centaurea
|accepted_authority=Linnaeus
|publications={{Treatment/Publication
|title=Sp. Pl.
|place=2: 909. 1753
|year=1753
}}, {{Treatment/Publication
|title=Gen. Pl. ed.
|place=5, 389. 1754
|year=1754
}}
|common_names=Knapweed;star thistle;cornflower;centaurée
|basionyms=
|synonyms={{Treatment/ID/Synonym
|name=Acosta
|authority=Adanson
|rank=genus
}} {{Treatment/ID/Synonym
|name=Cnicus
|authority=Linnaeus
|rank=genus
}} {{Treatment/ID/Synonym
|name=Grossheimia
|authority=Sosnowsky & Takhtajan
|rank=genus
}} {{Treatment/ID/Synonym
|name=Jacea
|authority=Miller
|rank=genus
}} {{Treatment/ID/Synonym
|name=Leucacantha
|authority=Nieuwland & Lunell
|rank=genus
}}
|hierarchy=Asteraceae;Asteraceae tribe Cardueae;Centaurea
|hierarchy_nav=<div class="higher-taxa"><div class="higher-taxon"><small>family</small>[[Asteraceae]]</div><div class="higher-taxon"><small>tribe</small>[[Asteraceae tribe Cardueae]]</div><div class="higher-taxon"><small>genus</small>[[Centaurea]]</div></div>
|etymology=Greek kentaurieon, ancient plant name associated with Chiron, a centaur famous for knowledge of medicinal plants
|volume=Volume 19
|mention_page=page 52, 57, 58, 67, 83, 84, 96, 171, 172, 176, 177
|treatment_page=
}}<!--

--><span class="statement" id="st-undefined" data-properties=""><b>Annuals,</b> biennials, or perennials, 20–300 cm, glabrous or tomentose. <b>Stems</b> erect, ascending, or spreading, simple or branched. <b>Leaves</b> basal and cauline; petiolate or sessile; proximal blade margins often ± deeply lobed, (spiny in <i>C. benedicta</i>), distal ± smaller, often entire, faces glabrous or ± tomentose, sometimes also villous, strigose, or puberulent, often glandular-punctate. <b>Heads</b> discoid, disciform, or radiant, borne singly or in corymbiform arrays. <b>Involucres</b> cylindric or ovoid to hemispheric. <b>Phyllaries</b> 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. <b>Receptacles</b> flat, epaleate, bristly. <b>Florets</b> 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. <b>Cypselae</b> ± barrel-shaped, ± compressed, smooth or ribbed, apices entire (denticulate in <i>C. benedicta</i>), glabrous or with fine, 1-celled hairs, attachment scars lateral (with or without elaiosomes); pappi 0 or ± persistent, of 1–3 series of smooth or minutely barbed, stiff bristles or narrow scales. <b>x</b> = 8, 9, 10, 11, 12, 13, 15.</span><!--

-->{{Treatment/Body
|distribution=Eurasia;n Africa;widely introduced worldwide.
|discussion=<p>Species ca. 500 (20 in the flora).</p><!--
--><p>Taxonomic limits of <i>Centaurea</i> 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 <i>Centaurea</i> into smaller genera or workable infrageneric taxa. The relations of several satellite genera have been controversial as well.</p><!--
--><p>Recent molecular phylogenetic studies (A. Susanna et al. 1995; N. Garcia-Jacas et al. 2000, 2001) have begun to clarify relationships within <i>Centaurea</i> and between <i>Centaurea</i> and other genera. These studies make it clear that <i>Centaurea</i> as traditionally defined is polyphyletic, and that generic boundaries should be realigned if monophyletic taxa are to be recognized. Some taxa traditionally included within <i>Centaurea</i> (e.g., the two native North American species, <i>Centaurea</i> americana and C. rothrockii) fall outside the redefined generic boundaries and are here treated in <i>Plectocephalus</i>. Others usually placed into segregate genera (e.g., Cnicus benedictus) are firmly nested within <i>Centaurea</i>. Because the type species of <i>Centaurea</i> (C. centaurium Linnaeus, an African species) falls outside the main lineage of the genus, a proposal has been made to conserve <i>Centaurea</i> 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 <i>Centaurea</i> clade.</p><!--
--><p>Although several <i>Centaurea</i> 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.</p><!--
--><p><i>Centaurea</i> aspera Linnaeus (rough star thistle) is known from nineteenth-century collections from ballast piles in New York; it does not appear to be established as a member of the North American flora. It can readily be distinguished from the similar <i>C. diluta</i>: the phyllary appendages are divided into palmately radiating clusters of short spines.</p><!--
--><p><i>Centaurea</i> babylonica Linnaeus has been reported from California as a waif (F. Hrusa et al. 2002); apparently it is not established as a permanent member of the flora. It is a tall (to 3 m), yellow-flowered <i>Centaurea</i> with numerous heads clustered in spiciform arrays. The phyllaries are leathery, and appendages are absent or reduced to spines 1 mm or shorter.</p><!--
--><p><i>Centaurea</i> cineraria Linnaeus (dusty miller), an Italian species known from casual garden escapes (California, Maryland, New York), probably is not permanently established as a member of the North American flora. It is a perennial with pinnately or bipinnately divided, densely gray-tomentose leaves, usually solitary, radiant heads somewhat larger than those of <i>C. stoebe</i>, and purple corollas.</p><!--
--><p><i>Centaurea</i> eriophora Linnaeus, reported from California and Colorado (J. T. Kartesz and C. A. Meacham 1999), would key below to <i>C. sulphurea</i>. It differs from <i>C. sulphurea</i> in having densely arachnoid-tomentose involucres. The California report is based on an early twentieth-century collection from Los Angeles County (A. Davidson 2334, UC). It is unlikely that this species is permanently established as a member of the California flora. The Colorado report is apparently erroneous, referenced to a report of Jacea pratensis Lamarck (= <i>Centaurea jacea</i> Miller), a wholly different plant, in W. A. Weber and R. C. Wittmann (1992).</p><!--
--><p>A population of <i>Centaurea</i> trichocephala M. Bieberstein ex Willdenow (featherhead or hairy-head knapweed) was found in the late 1970s in a degraded pasture in eastern Washington (B. F. Roché and C. T. Roché 1991). A weed-control program was instituted, and the plants were successfully eradicated. Although it is apparently not established anywhere in North America, C. trichocephala is listed as a noxious weed in Oregon. These plants resemble <i>C. phrygia</i> in having elongate, pectinate-fringed phyllary appendages. In C. trichocephala the linear-filiform, featherlike appendages are much narrower than the phyllary bodies. Plants of the species spread by horizontal roots. According to Roché and Roché, C. trichocephala is apparently self-sterile; the Oregon plants spread clonally and formed no seeds.</p><!--
--><p>Although Cnicus has usually been recognized as a distinctive monotypic genus, it has been merged into <i>Centaurea</i> 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 <i>Centaurea</i>.</p><!--
--><p>Excluded species:</p><!--
--><p><i>Centaurea</i> bovina. J. T. Kartesz and C. A. Meacham (1999) listed C. bovina Velenovský from Massachusetts, referencing Rhodora 1924, perhaps based on collections reported as <i>C. diffusa</i> from Norfolk County (C. H. Knowlton and W. Deane 1924). Knowlton and Deane made no mention of C. bovina. According to J. Dostál (1976), C. bovina differs from <i>C. diffusa</i> in having smaller involucres (6–7 mm versus 7–10 mm; 3.5 mm versus 4–5 mm diameter), and purple versus pink flowers). Examination of one of the Norfolk County collections (Churchill s.n., MIN) revealed no differences from <i>C. diffusa</i>.</p><!--
--><p>According to R. Angelo (pers. comm.), “The Kartesz citation is puzzling. This taxon [C. bovina] is not cited in the 1924 volume of Rhodora or anywhere in the first 50 years of Rhodora according to the index for that volume and our 50 year index (which is quite comprehensive).</p><!--
--><p>“Also, there are no specimens identified as this taxon in the New England Botanical Club (NEBC) herbarium or from Massachusetts in the Harvard University Herbaria collections. We also looked for re-identifications in the other taxa in <i>Centaurea</i> in the NEBC and found no specimens that were earlier identified as C. bovina.</p><!--
--><p>“The Vascular Plants of Massachusetts[...] (1999) of [B. A.] Sorrie and [P.] Somers does not list this taxon, nor does the Flora of the Northeast[...] (1999) by [D. W.] Magee and [H. E.] Ahles.”</p><!--
--><p><i>Centaurea</i> paniculata. According to our herbarium studies, reports of C. paniculata Linnaeus (Jersey knapweed) from North America are apparently referable to <i>C. stoebe </i>subsp.<i> micranthos</i>. <i>Centaurea</i> paniculata is quite similar to <i>C. stoebe</i> in habit; it differs clearly by its narrowly ovoid or cylindric heads.</p>
|tables=
|references=
}}<!--

--><div class="treatment-key">
==Key==
<div class="treatment-key-group">
  
{| class="wikitable fna-keytable"
|-id=key-0-1
|1
|Corollas yellow
|[[#key-0-2| > 2]]
|-id=key-0-1
|1
|Corollas white to pink, blue, or purple
|[[#key-0-6| > 6]]
|-id=key-0-2
|2
|Phyllary appendages broadly scarious, ± covering phyllary bodies, lacerate fringed, spineless or tipped by weak spines 1–2 mm
|[[Centaurea macrocephala|Centaurea macrocephala]]
|-id=key-0-2
|2
|Phyllary appendages spiny fringed, not covering phyllary bodies, tipped with spines 5–25 mm
|[[#key-0-3| > 3]]
|-id=key-0-3
|3
|Heads sessile, each closely subtended and ± concealed by involucrelike cluster of expanded, foliar bracts
|[[Centaurea benedicta|Centaurea benedicta]]
|-id=key-0-3
|3
|Heads evidently pedunculate, or if sessile, each not concealed by involucrelike cluster of expanded, foliar bracts
|[[#key-0-4| > 4]]
|-id=key-0-4
|4
|Corollas usually longer than 25 mm
|[[Centaurea sulphurea|Centaurea sulphurea]]
|-id=key-0-4
|4
|Corollas usually 10–20 mm
|[[#key-0-5| > 5]]
|-id=key-0-5
|5
|Central spines of principal phyllaries 5–10 mm
|[[Centaurea melitensis|Centaurea melitensis]]
|-id=key-0-5
|5
|Central spines of principal phyllaries 10–25 mm
|[[Centaurea solstitialis|Centaurea solstitialis]]
|-id=key-0-6
|6
|Principal phyllaries tipped with spines
|[[#key-0-7| > 7]]
|-id=key-0-6
|6
|Principal phyllaries not spine-tipped
|[[#key-0-11| > 11]]
|-id=key-0-7
|7
|Central spines of principal phyllaries 10–25 mm
|[[#key-0-8| > 8]]
|-id=key-0-7
|7
|Central spines of principal phyllaries usually 1–5 mm
|[[#key-0-9| > 9]]
|-id=key-0-8
|8
|Young leaves ± gray tomentose when young; involucre bodies 6–8 mm diam.; florets 25–40
|[[Centaurea calcitrapa|Centaurea calcitrapa]]
|-id=key-0-8
|8
|Young leaves minutely bristly, green; involucre bodies 8–14 mm diam.; florets many
|[[Centaurea iberica|Centaurea iberica]]
|-id=key-0-9
|9
|Involucres 8–15 mm diam
|[[Centaurea diluta|Centaurea diluta]]
|-id=key-0-9
|9
|Involucres 3–5 mm diam
|[[#key-0-10| > 10]]
|-id=key-0-10
|10
|Corollas 12–13 mm; involucres 10–13 mm
|[[Centaurea diffusa|Centaurea diffusa]]
|-id=key-0-10
|10
|Corollas 7–9 mm; involucres 7–8 mm
|[[Centaurea virgata|Centaurea virgata]]
|-id=key-0-11
|11
|Annuals
|[[#key-0-12| > 12]]
|-id=key-0-11
|11
|Perennials
|[[#key-0-13| > 13]]
|-id=key-0-12
|12
|Proximal leaves lanceolate, acute; phyllary appendages white to dark brown or black, teeth ± 1 mm; pappi 2–4 mm
|[[Centaurea cyanus|Centaurea cyanus]]
|-id=key-0-12
|12
|Proximal leaves oblong, obtuse; phyllary appendages silvery white to brown, teeth 1.5–2 mm; pappi 6–8 mm
|[[Centaurea depressa|Centaurea depressa]]
|-id=key-0-13
|13
|Phyllary appendages tapering to long, often recurved, pectinately dissected, filiform tips
|[[Centaurea phrygia|Centaurea phrygia]]
|-id=key-0-13
|13
|Phyllary appendages obtuse to acute, erect or ascending
|[[#key-0-14| > 14]]
|-id=key-0-14
|14
|Involucres 10–13 mm
|[[Centaurea stoebe|Centaurea stoebe]]
|-id=key-0-14
|14
|Involucres 15–25 mm
|[[#key-0-15| > 15]]
|-id=key-0-15
|15
|Phyllary appendages evidently decurrent along phyllary margins
|[[#key-0-16| > 16]]
|-id=key-0-15
|15
|Phyllary appendages not or only slightly decurrent along phyllary margins
|[[#key-0-17| > 17]]
|-id=key-0-16
|16
|Leaves decurrent, entire or remotely dentate, or proximal some- times pinnately lobed
|[[Centaurea montana|Centaurea montana]]
|-id=key-0-16
|16
|Leaves not decurrent, 1–2-pinnately divided or distal entire.
|[[Centaurea scabiosa|Centaurea scabiosa]]
|-id=key-0-17
|17
|Phyllary appendages roundish, seldom triangular, scarious, light to dark brown, ± undivided to irregularly lacerate
|[[#key-0-18| > 18]]
|-id=key-0-17
|17
|Phyllary appendages ± triangular, brown to black, ± wholly pectinately fimbriate; pappus present or absent
|[[#key-0-19| > 19]]
|-id=key-0-18
|18
|Pappus absent
|[[Centaurea jacea|Centaurea jacea]]
|-id=key-0-18
|18
|Pappus present, 3–5 mm, of many white bristles
|[[Centaurea diluta|Centaurea diluta]]
|-id=key-0-19
|19
|Heads discoid; peripheral florets not expanded, showy; pappus blackish, shorter than 1 mm; green parts of phyllaries ± totally covered by black appendages, involucres appearing totally black
|[[Centaurea nigra|Centaurea nigra]]
|-id=key-0-19
|19
|Heads radiant; peripheral florets expanded, showy, raylike; pappus absent or rudimentary, when present usually not black; green part of phyllaries sometimes evident or appendages light to dark brown
|[[#key-0-20| > 20]]
|-id=key-0-20
|20
|Heads relatively broad, the pressed involucres usually as wide as or wider than long; green parts of phyllaries usually fully covered by ± brown, variably pectinately fimbriate appendages, involucres light to dark brown
|[[Centaurea ×moncktonii|Centaurea ×moncktonii]]
|-id=key-0-20
|20
|Heads relatively narrow, the pressed involucres usually longer than wide; green parts of phyllaries not fully covered by black appendages, involucres black and green
|[[Centaurea nigrescens|Centaurea nigrescens]]
|}
</div></div><!--

-->{{#Taxon:
name=Centaurea
|author=David J. Keil;Jörg Ochsmann
|authority=Linnaeus
|rank=genus
|parent rank=tribe
|synonyms=Acosta;Cnicus;Grossheimia;Jacea;Leucacantha
|basionyms=
|family=Asteraceae
|distribution=Eurasia;n Africa;widely introduced worldwide.
|introduced=true
|reference=None
|publication title=Sp. Pl.;Gen. Pl. ed.
|publication year=1753;1754
|special status=
|source xml=https://jpend@bitbucket.org/aafc-mbb/fna-data-curation.git/src/eaa6e58056e40c9ef614d8f47aea294977a1a5e9/coarse_grained_fna_xml/V19-20-21/V19_205.xml
|tribe=Asteraceae tribe Cardueae
|genus=Centaurea
}}<!--

-->[[Category:Treatment]][[Category:Asteraceae tribe Cardueae]]