Centaurea calcitrapa |
Centaurea solstitialis |
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caltrops, centaurée chausse-trappe, chausse-trappe, purple knapweed, purple star-thistle, red star-thistle |
Barnaby star-thistle, centauré du solstice, golden starthistle, St. Barnaby's thistle, yellow cockspur, yellow knapweed, yellow star-thistle |
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Habit | Annuals, biennials, or short-lived perennials, 20–100 cm. | Annuals, 10–100 cm. |
Stems | 1–several, often forming rounded mounds, puberulent to loosely tomentose. |
simple or often branched from base, forming rounded bushy plants, gray-tomentose. |
Leaves | puberulent to loosely gray-tomentose, becoming ± glabrous, minutely resin-gland-dotted; proximal leaves petiolate, blades 10–20 cm, 1–3 times pinnately dissected, rosette with central cluster of spines; mid sessile, not decurrent, blades ovate, usually less than 10 cm, narrowly lobed; distal blades linear to oblong, entire to shallowly lobed. |
gray-tomentose and scabrous to short-bristly; basal and proximal cauline petiolate or tapered to base, usually absent at anthesis, blades 5–15 cm, margins pinnately lobed or dissected; cauline long-decurrent, blades linear to oblong, 1–10 cm, entire. |
Involucres | ovoid, 15–20 × 6–8 mm. |
ovoid, 13–17 mm, loosely cobwebby-tomentose or becoming glabrous. |
Florets | 25–40; corollas purple, all ± equal, 15–24 mm; sterile corollas slender. |
many; corollas yellow, all ± equal, 13–20 mm; sterile florets slender, inconspicuous. |
Inner phyllaries | appendages truncate, spineless. |
appendages scarious, obtuse or abruptly spine tipped. |
Heads | disciform, borne singly or in leafy cymiform arrays, sessile or short-pedunculate. |
disciform, borne singly or in open leafy arrays, long-pedunculate. |
Cypselae | white or brown-streaked, 2.5–3.4 mm, glabrous; pappi 0. |
dimorphic, 2–3 mm, glabrous, outer dark brown, without pappi, inner white or light brown, mottled; pappi of many white, unequal bristles 2–4 mm, fine. |
Principal | phyllaries: bodies greenish or stramineous, ovate, scarious-margined, appendages stramineous, spiny fringed at base, each tipped by a stout spreading spine 10–25 mm. |
phyllaries: bodies pale green, ovate, appendages stramineous to brown, each with palmately radiating cluster of spines, and stout central spine 10–25 mm. |
2n | = 20. |
= 16. |
Centaurea calcitrapa |
Centaurea solstitialis |
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Phenology | Flowering summer–autumn (Jun–Nov). | Flowering mostly summer–autumn (Jun–Oct), sometimes year-round in frostfree coastal habitats. |
Habitat | Pastures, fields, roadsides | Roadsides, fields, pastures, woodlands |
Elevation | 0–1700 m (0–5600 ft) | 0–2000 m (0–6600 ft) |
Distribution |
AL; AZ; CA; DC; FL; GA; IA; IL; MA; MD; NJ; NM; NY; OR; PA; UT; VA; WA; ON; Europe; Africa
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AZ; CA; CO; CT; DE; FL; IA; ID; IL; IN; KS; KY; MA; MD; MI; MN; MO; MT; NC; ND; NE; NH; NJ; NM; NV; NY; OH; OK; OR; PA; RI; SC; SD; TN; TX; UT; VA; WA; WI; WV; WY; AB; MB; ON; SK; s Europe [Widely introduced]
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Discussion | Centaurea calcitrapa is native to southern Europe and northern Africa. It is listed as a noxious weed in Arizona, California, Nevada, New Mexico, Oregon, and Washington. These plants are unpalatable and increase on rangelands as more desirable forage plants are consumed. Dense stands are impenetrable because of the vicious spines on the mature involucres. Centaurea ×pouzinii de Candolle, an apparently stabilized hybrid between Centaurea aspera (2n = 22) and C. calcitrapa (2n = 20), has been reported from California. A chromosome count of 2n = 42 has been reported from California material of this nothospecies (A. M. Powell et al. 1974). Centaurea ×pouzinii can be distinguished from C. calcitrapa by its shorter spines and by cypselae with a short pappus. Reports of C. calcitrapoides Linnaeus from North America are apparently based on this hybrid. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Centaurea solstitialis is a serious weed pest, especially in the western United States, where it has invaded millions of acres of rangelands, and it is listed as a noxious weed in eleven western states and two Canadian provinces. It is a strong competitor in infested areas, often forming dense colonies. It is very difficult to control or eradicate once it becomes established. In addition, yellow star-thistle is poisonous to horses; when ingested over a prolonged period it causes a neurological disorder called equine nigropallidal encephalomalacia, or “chewing disease.” Although its bitter taste and spiny heads usually deter grazing animals, horses sometimes will seek it out. Yellow star-thistle tends to spread in rangelands when more palatable plants are consumed. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Source | FNA vol. 19, p. 191. | FNA vol. 19, p. 193. |
Parent taxa | Asteraceae > tribe Cardueae > Centaurea | Asteraceae > tribe Cardueae > Centaurea |
Sibling taxa | ||
Name authority | Linnaeus: Sp. Pl. 2: 917. (1753) | Linnaeus: Sp. Pl. 2: 917. (1753) |
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