Centaurea calcitrapa |
Centaurea ×moncktonii |
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caltrops, centaurée chausse-trappe, chausse-trappe, purple knapweed, purple star-thistle, red star-thistle |
meadow knapweed, protean knapweed |
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Habit | Annuals, biennials, or short-lived perennials, 20–100 cm. | Perennials, 30–150 cm. |
Stems | 1–several, often forming rounded mounds, puberulent to loosely tomentose. |
1–few, erect or ascending, openly branched distally, villous to scabrous with septate hairs and loosely tomentose, ± glabrate. |
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. |
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, blades linear to lanceolate, gradually smaller, entire or dentate. |
Involucres | ovoid, 15–20 × 6–8 mm. |
ovoid to campanulate or hemispheric, 15–18 mm, usually ± as wide as high. |
Florets | 25–40; corollas purple, all ± equal, 15–24 mm; sterile corollas slender. |
40–100+, all fertile or the peripheral sterile; corollas purple (rarely white), those of sterile florets ± expanded and exceeding corollas of fertile florets, those of fertile florets 15–18 mm. |
Inner phyllaries | appendages truncate, spineless. |
tips truncate, irregularly dentate or lobed. |
Heads | disciform, borne singly or in leafy cymiform arrays, sessile or short-pedunculate. |
usually radiant (rarely discoid), in few-headed corymbiform arrays, borne on leafy-bracted peduncles. |
Cypselae | white or brown-streaked, 2.5–3.4 mm, glabrous; pappi 0. |
tan, 2.5–3 mm, finely hairy; pappi 0 or of many unequal, sometimes caducous bristles 0.5–1 mm. |
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 lanceolate to ovate, loosely tomentose or glabrous, usually concealed by expanded appendages, appendages erect, overlapping, light to dark brown, flat or ± concave, margins varying from coarsely dentate to pectinately dissected into ± wiry lobes. |
2n | = 20. |
= 22 (England), 44. |
Centaurea calcitrapa |
Centaurea ×moncktonii |
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Phenology | Flowering summer–autumn (Jun–Nov). | Flowering spring–fall (May–Nov). |
Habitat | Pastures, fields, roadsides | Roadsides, riverbanks, pastures, meadows, forest openings, waste areas |
Elevation | 0–1700 m (0–5600 ft) | 0–1000 m (0–3300 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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CA; CT; ID; IL; MA; ME; MI; MN; MO; MT; NH; NJ; NY; OH; OR; PA; RI; VA; VT; WA; WI; BC; NL; NS; ON; QC; Europe [Introduced in North America]
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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 ×moncktonii is native to Europe or originated in North America from European ancestry. Meadow knapweeds represent an array of mutually interfertile intermediates derived by hybridization and backcrossing among the various cytotypes of the Centaurea jacea complex. The plants variously combine features of C. jacea and C. nigra, and perhaps C. nigrescens as well. The hybrid complex includes both diploids and tetraploids. Extremes approach the parental types. Meadow knapweeds are often present without either parent in the immediate vicinity. They are considered to be noxious weeds in British Columbia, Idaho, Oregon, and Washington. Centaurea pratensis J. L. Thuillier, sometimes applied to plants that belong here, is not a legitimate name. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Source | FNA vol. 19, p. 191. | FNA vol. 19, p. 187. |
Parent taxa | Asteraceae > tribe Cardueae > Centaurea | Asteraceae > tribe Cardueae > Centaurea |
Sibling taxa | ||
Synonyms | C. debeauxii subsp. thuillieri, C. jacea var. pratensis, C. jacea subsp. ×pratensis, C. nigra var. radiata, C. thuillieri | |
Name authority | Linnaeus: Sp. Pl. 2: 917. (1753) | C. E. Britton: Bot. Soc. Exch. Club Brit. Isles 6: 172. (1921) |
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